Apelin peptides  and uses thereof

ABSTRACT

The disclosure relates to modified apelin polypeptides having increased stability against kallikrein, NEP and ACE2 degradation and/or potency relative to the native apelin-13 and apelin-17 polypeptides. Embodiments also disclose methods of using the polypeptides for treating cardiovascular disorders.

RELATED APPLICATION INFORMATION

This application is a continuation application of U.S. patentapplication Ser. No. 16/027,237 filed Jul. 3, 2018, which claimspriority to U.S. Provisional Patent Application No. 62/528,379, filedJul. 3, 2017. The entire contents of the foregoing applications areincorporated herein by reference, including all text, tables, sequencelisting and drawings.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has beensubmitted electronically in ASCII format and is hereby incorporated byreference in its entirety. Said ASCII copy, created on Sep. 25, 2018, isnamed UofAlberta0459694_ST25.txt and is 28.9 KB in size.

BACKGROUND

Apelin (APLN), the endogenous mammalian peptide ligand of the apelinreceptor has been indicated as a regulator of the cardiovascular system.Human apelin is a pre-proprotein of 77 amino acids(MNLRLCVQALLLLWLSLTAVCGGSLMPLPDGNGLEDGNVRHLVQPRGSRNGPGPWQGGRRKFRRQRPRLSHKGPMPF (SEQ ID NO: 6)), with a secretory signal sequencein the N-terminal region. After cleavage of the signal peptide at theendoplasmic reticulum, the remaining 55 amino acid residue may undergofurther cleavage to several active isoforms including a 36 amino acidpeptide corresponding to apelin sequence residues 42-77 (apelin-36,LVQPRGSRNGPGPWQGGRRKFRR-QRPRLSHKGPMPF, (SEQ ID NO:3)) (3), a 17 aminoacid peptide corresponding to the apelin sequence residues 61-77(apelin-17, KFRRQRPRLSHKGPMPF (SEQ ID NO:2)) (2) and a 13 amino acidpeptide corresponding to the apelin sequence residues 65-77 (apelin-13,QRPRLSHKGPMPF (SEQ ID NO:7)), which all possess a conserved C-terminalamino acid (FIG. 1). The apelin-13 fragment may also undergo subsequentpyroglutamylation at its N-terminal glutamine residue to provide (pyr¹)apelin-13 ((Pyr)RPRLSHKGPMPF (SEQ ID NO:1) (1).

Apelin pathway mediates a positive effect on cardiac contractility andvasodilator activity that counteracts angiotensin-II-inducedvasoconstriction. Moreover, apelin administration has been indicated toreduce the progression of cardiac hypertrophy, while apelin knockoutmice have been shown to be susceptible to heart failure. Apelin also hasa beneficial role in the cardiovascular system, such as initiatingvasodilation through a NO-mediated mechanism, positive inotropy,angiogenesis, and the prevention of myocardial ischemic reperfusioninjury.

Despite the beneficial physiological effects of the apelinergic system,the lifespan of apelin peptides is heavily regulated and limited viaproteolysis. The (pyr1) apelin-13 fragment (SEQ ID NO:1), for example,has been indicated as an endogenous ligand for the apelin receptor withan EC50 about 0.37 nM, while (pyr1) apelin-13 exhibits potent vasculareffects in vivo. However, (pyr1) apelin-13 stability is quite low inhuman plasma, with a t_(1/2) of about one minute.

Angiotensin converting enzyme 2 (ACE2) is a well-knownmonocarboxypeptidase that efficiently catalyzes the removal of theconserved C-terminal phenylalanine from apelin isoforms in vitro and invivo. Des-phenylalanine apelin isoforms behave as biased agonists byretaining native binding and forskolin-induced cAMP inhibition, butabolishing apelin receptor internalization and β-arrestin recruitment.Studies have shown that truncated peptides demonstrate a diminishedcapacity to lower blood pressure and have no ability to protect againstmyocardial ischemic reperfusion injury, making the C-terminal Pheresidue essential for full agonist activity. Therefore, there exists aneed to negate the impact of ACE2 degradation on apelin isoforms, and toimprove the overall stability of the apelin isoforms. Given thetherapeutic potential of (pyr1) apelin-13 and related apelin peptides,there is a continued interest in stabilizing the peptide structureswhile preserving their biological profiles.

SUMMARY

The present disclosure relates to peptide and peptide-like therapeuticagents for the treatment of various diseases and conditions related tothe apelin/apelin receptor system. In particular, the present disclosurerelates to apelin-based therapeutics and their use in treating variousdiseases and disorders of the cardiovascular system.

Embodiments disclosed herein relate to apelin peptides, in particular,apelin peptides comprising peptidomimetic of Formula (I):Z1-pGlu-aa2-aa3-aa4-aa5-aa6-aa7-aa8-aa9-aa10-aa11-aa12-aa13, orpharmaceutically acceptable salts thereof, wherein Z1 is H or a longchain moiety, wherein each of aa2, aa3, aa4, aa5, aa6, aa7, aa8, aa9,aa10, aa11, aa12, and aa13 is independently an amino acid, wherein: aa2comprises Arg or a conservative variant thereof; aa3 comprises Pro or aconservative variant thereof; aa4 comprises an amino acid or aconservative variant thereof selected from the group consisting of Arg,Arg-D, αMeArg and azaArg; aa5 comprises an amino acid or a conservativevariant thereof selected from the group consisting of Leu, NMeLeu,αMeLeu and azaLeu; aa6 comprises Ser or a conservative variant thereof;aa7 comprises His or a conservative variant thereof; aa8 comprises Lysor a conservative variant thereof; aa9 comprises Gly or a conservativevariant thereof; aa10 comprises Pro or a conservative variant thereof;aa11 comprises Nle or a conservative variant thereof, wherein Nlecomprises norleucine; aa12 comprises Aib or a conservative variantthereof, wherein Aib comprises α-aminoisobutyric acid; and aa13comprises paraBrPhe or a conservative variant thereof.

Embodiments disclosed herein relate to apelin peptides, in particular,apelin peptides comprising peptidomimetic of Formula (II):Z2-Lys-Phe-Arg-Arg-Gln-aa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa′15-aa′16-aa′17,or pharmaceutically acceptable salts thereof, wherein Z2 is H or a longchain moiety, wherein each of aa′6, aa′7, aa′8, aa′9, aa′10, aa′11,aa′12, aa′13, aa′14, aa′15, aa′16 and aa′17 is independently an aminoacid, wherein: aa′6 comprises Arg or a conservative variant thereof; aa6comprises Arg or a conservative variant thereof; aa′7 comprises Pro or aconservative variant thereof; aa′8 comprises an amino acid or aconservative variant thereof selected from the group consisting of Arg,Arg-D, αMeArg and azaArg; aa′9 comprises an amino acid or a conservativevariant thereof selected from the group consisting of Leu, NMeLeu,αMeLeu and azaLeu; aa′10 comprises Ser or a conservative variantthereof; aa′11 comprises His or a conservative variant thereof; aa′12comprises Lys or a conservative variant thereof; aa13 comprises Gly or aconservative variant thereof; aa′14 comprises Pro or a conservativevariant thereof; aa′15 comprises Nle or a conservative variant thereof,wherein Nle i comprises norleucine; aa′16 comprises Aib or aconservative variant thereof, wherein Aib comprises α-aminoisobutyricacid; and aa′17 comprises paraBrPhe or a conservative variant thereof.

Embodiments disclosed herein relate to methods of modulating an apelinpathway disorder in a subject comprising administering to the subject atherapeutically effective amount of an apelin peptide comprising apeptidomimetic of Formula (I) of claim 1 or Formula (II) of the presentdisclosure or pharmaceutically acceptable salts thereof.

Embodiments disclosed herein relate to methods of modulating vasculartone in a subject comprising administering to the subject an effectiveamount of an apelin receptor agonist comprising a peptidomimetic ofFormula (I) or Formula (II), or pharmaceutically acceptable saltsthereof.

Embodiments disclosed herein relate to methods of reducing cardiacreperfusion injury following myocardial infarction in a subjectcomprising administering to the subject an effective amount of an apelinreceptor agonist comprising a peptidomimetic of Formula (I) or Formula(II), or pharmaceutically acceptable salts thereof.

Embodiments disclosed herein relate to methods of reducing bloodpressure in a subject comprising administering to the subject aneffective amount of an apelin receptor agonist comprising apeptidomimetic of Formula (I) or Formula (II), or pharmaceuticallyacceptable salts thereof.

BRIEF DESCRIPTION OF DRAWINGS

Various embodiments of the present disclosure will be described hereinbelow with reference to the figures wherein:

FIG. 1 shows apelin isoforms: (pyr¹) apelin-13 fragment (SEQ ID NO:1)(1), apelin-17 (SEQ ID NO:2) (2), and apelin-36 (SEQ ID NO:3) (3), withidentified sites of NEP and ACE2 proteolytic degradation.

FIG. 2 illustrates certain syntheric modifications into both thepyr-1-apelin-13 A2,pGlu-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe (SEQ ID NO:4)(4), and apelin-17 A2,Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe(SEQ ID NO:5) (5), in accordance with embodiments of the presentdisclosure.

FIG. 3 is a synthetic reaction scheme showing the general SPPS approachfor the divergent syntheses of Arg/Leu modified apelin A2 peptides.

FIG. 4 is a synthetic scheme of dipeptide 22 for the preparation ofN-methyl leucine apelin A2 peptides 10 and 11.

FIG. 5 is a synthetic scheme of dipeptide 29 for the preparation ofα-methyl arginine apelin A2 peptides 12 and 13.

FIG. 6 is a synthetic scheme of dipeptide 33 for the preparation ofα-methyl leucine apelin A2 peptides 14 and 15.

FIG. 7 is a synthetic scheme of dipeptide 39 for the preparation ofaza-arginine apelin A2 peptides 16 and 17.

FIG. 8 is a synthetic scheme of dipeptide 45 for the preparation ofaza-arginine apelin A2 peptides 18 and 19.

FIGS. 9 A-B demonstrate in vitro NEP degradation trends forpyr-1-apelin-13 peptides (FIG. 9A) and apelin-17 peptides (FIG. 9B)according to embodiments of the disclosure.

FIGS. 10 A-H demostrates in vivo systolic (SBP, FIG. 10A/FIG. 10E),diastolic (DBP, FIG. 10B/FIG. 10F) and mean arterial blood pressure(MABP, FIG. 10C/FIG. 10G) and heart rate analyses (HR, FIG. 10D/FIG.10H) following injection of pyr-1-apelin-13 A2 (left) and apelin-17 A2(right) peptides in anesthetized mice.

FIGS. 11 A-E demostrates ex vivo heart assessment: heart rate (HR, FIG.11 A); maximum derivative of change in systolic pressure over time (maxdP/dt, FIG. 11 B); left ventricle developed pressure (LVDP, FIG. 11 C),minimum derivative of change in diastolic pressure over time (min dP/dt,FIG. 11 D); and rate-pressure product (RPP, FIG. 11 E), usingLangendorff experiments following reperfusion of saline (negativecontrol, sham), native 2 (positive control) and peptides 11, 17-19 aftera 30-minute period of ischemia.

FIG. 12 shows the KLKB1 cleavage between Arg3 and Arg4 of the nativeApelin-17 (2).

FIGS. 13 A-B show the breakdown-fragments 1-3 (FIG. 13A) and 4-17 FIG.13B) after plasma incubation of apelin-17A2 (peptide 5).

FIGS. 14A-G show the concentration response curves of apelin peptides ofthe certain embodiments of the disclosure.

FIGS. 15A-D demostrates in vivo systolic (SBP, FIG. 15B), diastolic(DBP, FIG. 15C) and mean arterial blood pressure (MABP, FIG. 15A) andheart rate analyses (HR, FIG. 15D) following injection of Apelin-NMe17A2(peptide 11), and apelin peptides 55-59 in anesthetized mice.

FIGS. 16A-B demostrates blood pressure data of KLKB1 fragments 54 and55.

FIG. 17A-B are micrographs of the cross-sectional area of theintimal/lumen with Verhoeff-van Gieson-stained saline-treated controlcarrier compared to an apelin peptide (11) treated coronary arteries.

FIG. 18 is a bar chart of showing the ratio of luminal/lumen areas forcoronary arteries 2 and 6 weeks after heart transplant of the model.

FIG. 19 is a curve showing the survival rate of mortality due to aorticrupture in the indicated groups.

FIG. 20 shows representative ultrasound images of the abdominal aortaand averaged measurement for abdominal aorta diameter (during systoleand diastole), and Aortic Expansion Index, a measure of aortic wallcompliance in Ldlr^(−/−) mice that received vehicle or Ang II for 4weeks, or Ang II+apelin peptide 11. n=8 per group.

FIG. 21 shows representative images of immunostaining for abdominalaorta sections for calponin (SMC, red), TUNEL (green), DAPI (blue) andelastin fibers' autofluorescence (green) in the indicated group.Averaged quantification for Calponin levels (measure of viable SMCs),and apoptotic cells (TUNEL-positive) for each group is shown on theright.

FIG. 22 shows representative Western blot for cleaved and total caspase3, and averaged cleaved-to-total ratio for Caspase 3.

FIG. 23 shows representative immunostaining for ACE2 and averagedquantification in the abdominal aorta of Ldlr−/− mice receiving saline,Ang II or Ang II+apelin peptide 11, n=6 per group.

FIG. 24 shows representative Western blot and averaged quantificationfor ACE2 in abdominal aorta of Ldlr^(−/−) mice receiving saline, Ang IIor Ang II+apelin peptide 11. Aortic protein from Ace2^(−/−) mouse wasused as the negative control.

FIG. 25 shows DHE fluorescence and NADPH oxidase activity showingsuppression of oxidative stress by the apelin peptide 11. *p<0.05compared to vehicle group. A.U.=arbitrary units. Averaged valuesrepresent Mean±SEM.

DETAILED DESCRIPTION

As used herein, the native human full length 77 amino acid (SEQ ID NO:6) may be referred to generally as “apelin” or “APLN,” while “apelinpeptides” will be used in reference to peptides encompassing bothnaturally occurring cleavage products of apelin such as apelin-36,apelin 17, apelin-13, pyr¹ apelin-13, as well as stabilized syntheticpeptide derivatives, in accordance with embodiments herein.

The role of APLN and the therapeutic use of the novel stabilized apelinpeptides disclosed herein in myocardial infarction (MI) andischemia-reperfusion (IR) injury is provided. Myocardial APLN levelswere reduced in subjects with ischemic heart failure. Loss of APLNincreased MI-related mortality, infarct size, and inflammation withsubstantial reductions in pro-survival pathways resulting in greatersystolic dysfunction and heart failure. APLN deficiency decreasedvascular sprouting, impaired sprouting of human endothelial progenitorcells and compromised in vivo myocardial angiogenesis. Lack of APLNenhanced susceptibility to ischemic injury and compromised functionalrecovery following ex vivo and in vivo IR injury. Advantageously, thestabilized apelin peptides disclosed herein may provide improved apelinproteolytic stability against NEP and improved resistance to angiotensinconverting enzyme 2 (ACE2) cleavage and may mimic the function of APLN,while demonstrating protection against ex vivo and in vivo myocardial IRinjury linked to greater activation of survival pathways and promotionof angiogenesis. The short half-life of native apelin peptides (Japp AG, et al. Circulation. 121:1818-1827, (2010); Vickers C, et al. J BiolChem. 277:14838-14843, (2002); Japp A G, et al. J Am Coil Cardiol.52:908-913, (2008)) prompted the development of the apelin peptidesdisclosed herein which are more potent and less susceptible todegradation.

Since the APLN system is compromised in human heart failure (Chen M. M.,et al. Circulation. 108:1432-1439, (2003); Chong K S, et al. Eur J HeartFail. 8:355-360, (2006)), the integrative physiological role of the APLNsystem indicates that enhancing apelin action may serve to minimizemyocardial ischemic damage and the progression to advanced HF (hearfailure disease). Enhancing apelin action represents a new approach forthe treatment of ischemic heart failure.

As discussed, there exists a need to negate the impact of ACE2degradation on apelin isoforms, and to improve the overall stability ofthe apelin isoforms. To negate the impact of ACE2 degradation on apelinisoforms, an ACE2 resistant ‘A2’ C-terminus may be incorporated into thepeptidomimetic of the presence embodiments. The ACE2 resistant ‘A2’C-terminus denotes the last three amino acids of the apelin peptides. Insome embodiments, the peptidomimetic of the present embodimentscomprises unnatural residues substituted at the C-terminal Met-Pro-Pheportion of (pyr¹) apelin-13 (SEQ ID NO:1). In some embodiments, thepeptidomimetic of the present embodiments comprises unnatural residuessubstituted at the C-terminal Met-Pro-Phe portion of apelin-17. The term“apelin A2 peptides,” as used herein, refers to peptides compriseunnatural residues substituted at the C-terminal Met-Pro-Phe.

To further improve the overall stability of the apelin isoforms, it isnecessary to stabilize, or to improve the metalloprotease neutralendopeptidase 24.11 (neprilysin, NEP) stability. The inventors of thepresent disclosure discovered that the NEP has a role in the in vitroproteolysis of apelin. NEP is a significant protease implicated in thedegradation and inactivation of vasoactive peptides bradykinin,angiotensins, atrial natriuretic factor (ANP), and endothelins inaddition to many other peptide hormones in other organ systems. The siteof NEP proteolysis may be structurally and functionally an essentialfeature for apelin binding and subsequent physiological activity.Without being bound by theory, the amino acid residues surrounding thesite of NEP proteolysis (the ‘RPRL’ motif) has an enhanced rigidity andis suggested to induce a p-turn conformation upon binding (Langelaan, etal. Biochemistry 48:537-548 (2009)), and the two Arg residues have beenproposed to form key electrostatic interactions with acidic amino acidson the exterior of the apelin receptor to facilitate ligand binding(Gerbier, R., et al., FASEB J.: 29, 314-322 (2015)).

The inventors of the present disclosure discovered a way to improveapelin proteolytic stability against NEP while at the same time negatingthe impact of ACE2 degradation on apelin isoforms. This approachincludes altering the amino acids residues surrounding both the NEPcleavage site and the ACE2 degradation site. FIG. 1 shows apelinisoforms: (pyr¹) apelin-13 fragment (SEQ ID NO:1) (1), apelin-17 (SEQ IDNO:2) (2), and apelin-36 (SEQ ID NO:3) (3), with identified sites of NEPand ACE2 proteolytic degradation. In certain embodiments, the disclosureprovides peptidomimetic comprises unnatural residues substituted at theC-terminal Met-Pro-Phe portion. In certain embodiments, the disclosureprovides peptidomimetic comprises unnatural residues substituted at theC-terminal Met-Pro-Phe portion and optionally at any one or more ofamino acids at the “RPRL” motif (e.g., amino acid 2 “aa2”, amino acid 3“aa3”, amino acid 4 “aa4”, and/or amino acid 5 “aa5”) of (pyr¹)apelin-13. In certain embodiments, apelin peptides comprisingpeptidomimetic of Formula (I), wherein Z1 is H, having the followingformula: pGlu-aa2-aa3-aa4-aa5-aa6-aa7-aa8-aa9-aa10-aa11-aa12-aa13, orpharmaceutically acceptable salts thereof, wherein aa2 to aa13 aredefined herein. pGlu refers to pyroglutamic acid.

In certain embodiments, the disclosure provides peptidomimetic comprisesunnatural residues substituted at the C-terminal Met-Pro-Phe portion andoptionally at any one or more of amino acids at the RPRL motif (e.g.,amino acid 6 “aa′6”, amino acid 7 “aa′7”, amino acid 8 “aa′8”, and/oramino acid 9 “aa′9”) of apelin-17. In certain embodiments, thedisclosure provides apelin peptides comprising peptidomimetic of Formula(II), wherein Z2 is H, having the following formula:Lys-Phe-Arg-Arg-Gln-aa′6-aa′7-aa′8-aa′9-aa10-aa′11-aa′12-aa′13-aa′14-aa′15-aa′16-aa′17,or pharmaceutically acceptable salts thereof, wherein aa″9 to aa″20 aredefined herein.

The inventors of the present disclosure further discovered that thehuman plasma kallikrein (KLKB1) also has a role in the in vitroproteolysis of apelin. The inventors discovered that KLKB1 cleaves afterthe first three N-terminal amino acids (KFR) of the apelin-17 (i.e.,cleavage between Arg3-Arg4). The KLKB1 cleavage produces the C-terminal14-mer lacking the polar basic KFR head group. FIG. 12 shows the KLKB1cleavage between Arg3 and Arg4 of the native Apelin-17 (2).

In the human body, KLKB1 circulates as zymogen bound tohigh-molecular-weight kininogen and is activated by coagulation factorXIIa. (Kaplan, et. al.; Bradykinin formation. Plasma and tissue pathwaysand cellular interactions. Clin. Rev. Allergy Immunol. 1998, 16,403-429.). Once activated, KLKB1 possesses a trypsin like activity,cleaving at a basic residue in P1 position (Arg), whereas the bulkyhydrophobic Phe side chain at P2 can be accommodated in the S2 pocket ofthis enzyme. (Tang, et. al.; Expression, crystallization, andthree-dimensional structure of the catalytic domain of human plasmakallikrein. J. Biol. Chem. 2005, 280, 41077-41089.).

To improve apelin in vivo half-life, the inventors of the presentdisclosure discovered that this can be accomplished by the attachment ofa long chain moiety to the N-terminus of the apelin A2 peptides.Examples of long chain moieties and techniques to increase plasmahalf-life include, but are not limited to, N-terminal fatty acid chain(PALMitoylation), and polyethylene glycol chain (PEGylation), XTEN (an83.5 kDa) recombinant polypeptide consisting only of the amino acidsAla, Asp, Gly Pro, Ser, and Thr, detran conjugation, HESylation(Hydroxyethyl Starch, HES, is a modified natural polymer obtained bycontrolled hydroxyethylation of the plant polysaccharide amylopectin),polysialylation, HAylation, N- and O-Glycosylation, and lipidation, allof which are disclosed in Witteloostuijn, et. al., “Half-life extensionof biopharmaceuticals using chemical methods: alternatives toPEGylation;” ChemMedChem 2016, 11, 2474-2495, the disclosure of which isincorporated herein by reference in its entirety.

In certain embodiments, the disclosure provides apelin peptidescomprising peptidomimetic of Formula (I) having the following formula:Z1-pGlu-aa2-aa3-aa4-aa5-aa6-aa7-aa8-aa9-aa10-aa11-aa12-aa13, orpharmaceutically acceptable salts thereof, wherein Z1 is a long chainmoiety, wherein aa2 to aa13 are defined herein. In some embodiments, Z1is PALM or PEG.

In certain embodiments, the disclosure provides apelin peptidescomprising peptidomimetic of Formula (II) having the following formula:Z2-Lys-Phe-Arg-Arg-Gln-aa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa15-aa′16-aa17,or pharmaceutically acceptable salts thereof, wherein Z2 is a long chainmoiety, wherein aa′6 to aa′17 are defined herein. In some embodiments,Z2 is PALM or PEG.

In some embodiments, PALM may be

wherein n is from 8 to 20, from 10 to 18, or from 12 to 16. In someembodiments, any one or more carbon atom of the PALM may beindependently optionally substituted with a lower alkyl (e.g., methyl,ethyl, or propyl), PEG may be linear or branched and the end groups maybe either a hydroxyl group, amino group, a methoxy group, or aprotecting group, such as, Fmoc (fluorenylmethyloxycarbonyl), Boc(tert-butyloxycarbonyl), and the like.

In some embodiments, PEG is

wherein m is from 3 to 10, from 4 to 8, or from 5 to 7, wherein W may beH, a lower alkyl (e.g., methyl, ethyl, propyl, etc.), or a protectinggrou. In some embodiments, PEG is Fmoc-NH(CH₂)_(p)—, wherein p is 1 to5, or 2 to 4. In a specific embodiment, PEG is

Both the PEG and PALM groups are attached to the apelin peptide via anamide bond through the N-terminus. By way of example, the followingillustrates that the PALM group attaches to the N-terminus amino acidthrough an amide bond:

In specific embodiments, the disclosure provides specific apelinpeptides having the following structures:

Compound No. R3 R4  5 NH₂-Lys-Phe-Arg H 11 NH₂-Lys-Phe-Arg CH₃ 54 H H 55H CH₃ 56 PALM-Lys-Phe-Arg H 57 PEG-Lys-Phe-Arg CH₃ 58 PALM-Lys-Phe-Arg H59 PEG-Lys-Phe-Arg CH₃

In some embodiments, the disclosure provides apelin peptide (54):

(SEQ ID NO: 35) Arg-Gln-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (55):

(SEQ ID NO: 36) Arg-Gln-Arg-Pro-Arg-NMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (56):

(SEQ ID NO: 37) PALM-Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (57):

(SEQ ID NO: 38) PEG-Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (58):

(SEQ ID NO: 39) PALM-Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-NMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (59):

(SEQ ID NO: 40) PEG-Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-NMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide:

(SEQ ID NO: 41) PALM-Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-D-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide:

(SEQ ID NO: 42) PALM-Lys-Phe-Arg-Arg-Gln-Arg-Pro-αMeArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide:

(SEQ ID NO: 43) PALM-Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-αMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide:

(SEQ ID NO: 44) PALM-Lys-Phe-Arg-Arg-Gln-Arg-Pro-azaArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide:

(SEQ ID NO: 45) PALM-Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-azaLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide:

(SEQ ID NO: 46) PEG-Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-D-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide:

(SEQ ID NO: 47) PEG-Lys-Phe-Arg-Arg-Gln-Arg-Pro-αMeArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide:

(SEQ ID NO: 48) PEG-Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-αMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide:

(SEQ ID NO: 49) PEG-Lys-Phe-Arg-Arg-Gln-Arg-Pro-azaArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide:

(SEQ ID NO: 50) PEG-Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-azaLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

The term “peptidomimetic,” as used herein, refers to a peptide-likemolecule that has the activity of the peptide upon which it isstructurally based. A peptidomimetic includes the substitution of one ormore naturally occuring amino acids for any chemically modified aminoacids, individual unnatural amino acids, peptide-like moleculescontaining non-naturally occurring amino acids, and peptoids, and havean activity of the peptide upon which the peptidomimetic is derived(see, for example, Goodman and Ro, Peptidomimetics for Drug Design, in“Burger's Medicinal Chemistry and Drug Discovery” Vol. 1 (ed. M. E.Wolff; John Wiley & Sons (1995), pages 803-861).

The term “amino acid,” as used herein, refers to naturally occurring andsynthetic amino acids, as well as amino acid analogs and amino acidmimetics that function in a manner similar to the naturally occurringamino acids. Naturally occurring amino acids are those encoded by thegenetic code, as well as those amino acids that are later modified,e.g., hydroxyproline, γ-carboxyglutamate, selenocysteine, pyrrolysine,and O-phosphoserine. “Amino acid analogs” refers to compounds that havethe same basic chemical structure as a naturally occurring amino acid,i.e., an a carbon that is bound to a hydrogen, a carboxyl group, anamino group, and an R group, e.g., homoserine, norleucine, methioninesulfoxide, methionine methyl sulfonium. Such analogs have modified Rgroups (e.g., norleucine) or modified peptide backbones, but retain thesame basic chemical structure as a naturally occurring amino acid. Aminoacid mimetics refers to chemical compounds that have a structure that isdifferent from the general chemical structure of an amino acid, but thatfunctions in a manner similar to a naturally occurring amino acid. Aminoacids may be referred to herein by either their commonly known threeletter symbols or by the one-letter symbols recommended by the IUPAC-IUBBiochemical Nomenclature Commission. Nucleotides, likewise, may bereferred to by their commonly accepted single-letter codes.

The number after “amino acid” or “aa” or aa′” denotes the position ofthe amino acid residue in the polypeptide chain when counted from theamino terminal.

The terms “compounds,” “peptides,” and “peptidomimetic” are usedinterchangeably in the disclosure.

In some of such embodiments, the peptidomimetics may be selected toprovide non-hydrolyzable residues at these positions. Non-naturalpeptidomimetic residues may include, without limitation, D-amino acids,beta amino acids, homo amino acids, proline derivatives,para-substituted phenylalanines, amino alcohols, N-substituted amides,bridging amides, quaternary alpha amino acids, N-alkyl amino acids,alpha-alkyl amino acids, and aza peptides. D-amino acids involve themirror image of the naturally occurring L-isomers, which are mostly toincrease resistance against a range of degradation enzymes. Homo aminoacids include the addition of a methylene (CH₂) group to the α-carbon ofan amino acid, which are used to creating peptides that may have alteredbiological characteristics, such as enhanced biological activity orbetter biological stability. N-alkyl amino acids are amino acids thatcarry an alkyl group at the nitrogen instead of a proton. Introducing anN-alkyl amino acid (exemplified by methylation) may create a stericallyhindered environment about a susceptible amide bond, which may increasethe enzymatic stability of a peptide, thus increasing its biologicalhalf-life. Substitution with N-alkyl amino acids may also improvepeptidase stability and enhance intestinal permeability. Alpha-alkylamino acids are amino acids in which the proton on the α-carbon atom ofthe natural original (in between the amino and carboxy group) has beensubstituted by an alkyl group. Alpha-methyl amino acids are stable toracemization/epimerization since there is no longer the possibility forabstracting the α-proton. Bridging amide and aza peptide are strategiesfor stabilizing amide bonds.

In certain embodiments, peptidomimetics disclosed herein may modify anyamino acid residues about an amide bond according to the followingchemical structural modifications to enhance stability against enzymatic(or non-enzymatic) hydrolytic activity as indicated in Scheme I. Oneskilled in the art will appreciate that any of these techniques may beused in combination and that any other amide stabilizing strategies maybe employed. R₁ and R₂ shown in Scheme I denote the side chains of theamino acids according to the present embodiments. Scheme I illustratesthe modification by substituting H with a methyl group. However, oneskilled in the art will appreciate that the use of methyl functionalgroups in Scheme I is merely exemplary and that other functionalchemical moieties may fulfill substantially the same role.

By way of example only, a peptidomimetic of pyr-1-apelin-13 A2 peptidehaving the formula:pGlu-aa2-aa3-aa4-aa5-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe (SEQ IDNO:52), a peptidomimetic of apelin-17 A2 peptide having the formula:Lys-Phe-Arg-Arg-Gln-aa′6-aa′7-aa′8-aa′9-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe(SEQ ID NO:53), and a peptidomimetic of N-terminus modified apelin-17 A2peptide having the formula:Z2-Lys-Phe-Arg-Arg-Gln-aa′6-aa′7-aa′8-aa′9-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe(SEQ ID NO:54) are shown below identifying the ACE2 resistant ‘A2’C-terminus Nle11, Aib12, and para-BrPhe13 amino acid substitutions andNle15, Aib16, and para-BrPhe17 amino acid substitutions respectively.

where Z2 is a long chain moiety as defined herein.

In some embodiments, the pyr-1-apelin-13 A2 peptide (SEQ ID NO: 4)includes substitution of native methionine for norleucine at amino acid11 (aa11). In some embodiments, the apelin-17 A2 peptide (SEQ ID NO: 5)includes substitution of native methionine for norleucine at amino acid15 (aa′15). Without being bound by theory, the inventors believe thatthe native methionine residue is susceptible to oxidation. Thus,replacement with a simple hydrophobic residue may serve to circumventthis oxidative problem. One skilled in the art will appreciate thatsubstantially similar residues can replace norleucine by conservativesubstitution to provide an apelin peptide with substantially similarenhancement in stability. For example, other residues that may functionin a manner similar to norleucine may include alanine, homoalanine,valine, leucine, and isoleucine.

Similarly, the inventors believe that a modest electron withdrawinggroup on C-terminal Phe may enhance apelin stability and/or activity.Thus, the bromo on Phe may be replaced with other electron withdrawinggroups to similar effect. Such groups may include, without limitation,chloro, nitro, ester, and the like. In certain embodiments, the electronwithdrawing group need not appear in the para position, although from asynthetic standpoint this may be one of the easier positions to modify.In some embodiments, the pyr-1-apelin-13 A2 peptide (SEQ ID NO: 4)includes substitution of native phenylanlanine for bromophenylanlanine,BrPhe (e.g., orth-BrPhe, meta-BrPhe, para-BrPhe) at amino acid 13(aa13). In some embodiments, the apelin-17 A2 peptide (SEQ ID NO: 5)includes substitution of native phenylanlanine for bromophenylanlanine,BrPhe (e.g., orth-BrPhe, meta-BrPhe, para-BrPhe) at amino acid 17(aa′17).

In some embodiments, the pyr-1-apelin-13 A2 peptide (SEQ ID NO: 4)includes substitution of native proline for aminoisobutyryl (Aib) atamino acid 12 (aa12). In some embodiments, the apelin-17 A2 peptide (SEQID NO: 5) includes substitution of native proline for aminoisobutyryl(Aib) at amino acid 16 (aa′16). The sterically hindered aminoisobutyryl(Aib) residue present in the apelin peptides may slow C-terminalhydrolytic processes. Other hindered alpha amino acids may achievenominally the same effect. Thus, for example, any alpha,alpha-dialkylamino acid may be employed for this purpose. Thepreparation and coupling of hindered amino acids has been described inFu et al. J. Org. Chem. 66(21):7118-24 (2001), which is incorporatedherein by reference in its entirety.

In similar embodiments, such substitutions as decribed above may beintroduced into apelin-36 or even in the native full apelin proteinhaving 77 amino acid residues. Those skilled in the art will appreciatethat with the full length apelin protein, non-linear syntheticstrategies for protein preparation may be advantageous. Such proteinsmay also be achieved by incorporation of unnatural amino acids byengineering the requisite tRNA for its incorporation in a biosynthesisapproach. Such methods are well known to those skilled in the art.

In some embodiments, apelin peptides comprising serine may be stabilizedagainst the activity of serine proteases. In some such embodiments, theserine residue may be replaced with homoalanine, for example. Otherconservative substitutions for serine may be employed including anyneutral alkyl substituted amino acids such as alanine, leucine, orisoleucine. Other modifications may include the blocking of the serinehydroxyl group, such as by formation of a methyl ether.

Thus, N-alkylation (exemplified by methylation), C-quaternization (alsoexemplified by methylation) or both may be employed to create asterically hindered environment at a susceptible amide bond. Also shownare bridging amide and aza peptide strategies for stabilizing amidebonds. One skilled in the art will appreciate that any of thesetechniques may be used in combination and that any other amidestabilizing strategies may be employed.

In some embodiments, the peptidomimetic contains an ACE2 resistant ‘A2’C-terminus Nle, Aib, and para-BrPhe amino acid substitutions.

In embodiments, the present disclosure provides peptidomimetic withenhanced stability to NEP based on the apelin ‘A2’ peptides of (pyr1)apelin-13 A2 (SEQ ID NO:4)(4) and apelin-17 A2 (SEQ ID NO:5)(5). FIG. 2illustrates certain syntheric modifications of both the pyr-1-apelin-13A2 (SEQ ID NO:4) (4) and apelin-17 A2 (SEQ ID NO:5) (5), in accordancewith embodiments of the present disclosure. The modifications includereplacing the dipeptide Arg/Leu with various dipeptides as shown in FIG.2 to produce apelin peptides (8)-(19).

In some embodiments, the disclosure provides apelin peptide (8):

(SEQ ID NO: 24) pGlu-Arg-Pro-Arg-D-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (9):

(SEQ ID NO: 25) Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-D-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (10):

(SEQ ID NO: 26) pGlu-Arg-Pro-Arg-NMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (11):

(SEQ ID NO: 27) Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-NMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (12):

(SEQ ID NO: 28) pGlu-Arg-Pro-aMeArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (13):

(SEQ ID NO: 29) Lys-Phe-Arg-Arg-Gln-Arg-Pro-aMeArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (14):

(SEQ ID NO: 30) pGlu-Arg-Pro-Arg-aMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (15):

(SEQ ID NO: 31) Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-aMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (16):

(SEQ ID NO: 51) pGlu-Arg-Pro-azaArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (17):

(SEQ ID NO: 32) Lys-Phe-Arg-Arg-Gln-Arg-Pro-azaArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (18):

(SEQ ID NO: 33) pGlu-Arg-Pro-Arg-azaLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, the disclosure provides apelin peptide (16):

(SEQ ID NO: 34) Lys-Phe-Arg-Arg-Gln-Arg-Pro-Arg-azaLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.

In some embodiments, synthetic modifications may be made at any one ormore amino acids of the “RPRL” motif portion of the apelin ‘A2’peptides. In some embodiments, synthetic modifications may be made atany one or more amino acid 2, amino acid 3, amino acid 4, and/or aminoacid 5 (aa2, aa3, aa4 and/or aa5) of the pyr-1-apelin-13 A2 peptide (SEQID NO: 4). In some embodiments, synthetic modifications may be made atany one or more amino acid 6, amino acid 7, amino acid 8, and/or aminoacid 9 (aa′6, aa′7, aa′8 and/or aa′9) of the apelin-17 A2 peptide (SEQID NO: 5).

In embodiments, the peptidomimetic of Formula (I):Z1-pGlu-aa2-aa3-aa4-aa5-aa6-aa7-aa8-aa9-aa10-aa11-aa12-aa13, orpharmaceutically acceptable salts thereof, wherein Z1 is defined herein,wherein the sequence aa2-aa3-aa4-aa5-aa6-aa7-aa8-aa9-aa10-aa11-aa12-aa13is any one of the sequences listed in Table 1.

In embodiments, the peptidomimetic of Formula (II):Z2-Lys-Phe-Arg-Arg-Gln-aa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa′15-aa′16-aa′17,or pharmaceutically acceptable salts thereof, wherein Z2 is definedherein, wherein the sequenceaa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa′115-aa′16-aa′17 isany one of the sequences listed in Table 1.

TABLE 1 Arg-Pro-Arg-D-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe (Seq ID NO: 12)Arg-Pro-Arg-NMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe (Seq ID NO: 13)Arg-Pro-aMeArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe (Seq ID NO: 14)Arg-Pro-Arg-aMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe (Seq ID NO: 15)Arg-Pro-azaArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe (Seq ID NO: 16)Arg-Pro-Arg-azaLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe (Seq ID NO: 17)

In embodiments, the peptidomimetic of Formula (I):Z1-pGlu-aa2-aa3-aa4-aa5-aa6-aa7-aa8-aa9-aa10-aa11-aa12-aa13, orpharmaceutically acceptable salts thereof, wherein Z1 is defined herein,wherein the sequence aa2-aa3-aa4-aa5-aa6-aa7-aa8-aa9-aa10 is any one ofthe sequences listed in Table 2.

In embodiments, the peptidomimetic of Formula (II):Z2-Lys-Phe-Arg-Arg-Gln-aa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa′115-aa′16-aa′17,or pharmaceutically acceptable salts thereof, wherein Z2 is definedherein, wherein Z2 is defined herein, wherein the sequenceaa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14 is any one of thesequences listed in Table 2.

TABLE 2 Arg-Pro-Arg-D-Leu-Ser-His-Lys-Gly-Pro (Seq ID NO: 18)Arg-Pro-Arg-NMeLeu-Ser-His-Lys-Gly-Pro (Seq ID NO: 19)Arg-Pro-aMeArg-Leu-Ser-His-Lys-Gly-Pro (Seq ID NO: 20)Arg-Pro-Arg-aMeLeu-Ser-His-Lys-Gly-Pro (Seq ID NO: 21)Arg-Pro-azaArg-Leu-Ser-His-Lys-Gly-Pro (Seq ID NO: 22)Arg-Pro-Arg-azaLeu-Ser-His-Lys-Gly-Pro (Seq ID NO: 23)

In embodiments, the peptidomimetic disclosed herein comprises a suitablesequence having at least 80%, at least 85%, at least 90% or at least 95%identical to any one of the sequences disclosed in Table 1 or 2. Inembodiments, the peptidomimetic disclosed herein comprises a suitablesequence having at least 80%, at least 85%, at least 90% or at least 95%to any one of the sequences disclosed in Table 1 or 2, wherein a desiredfunction of the peptidomimetic is conserved or retained.

The term “percent identical” refers to sequence identity between twoamino acid sequences. Identity can be determined by comparing a positionin each sequence which may be aligned for purposes of comparison. Whenan equivalent position in the compared sequences is occupied by the sameamino acid, then the molecules are identical at that position. When theequivalent site is occupied by the same or a similar amino acid residue(e.g., similar in steric and/or electronic nature), then the moleculescan be referred to as homologous (similar) at that position. Expressionas a percentage of homology, similarity, or identity refers to afunction of the number of identical or similar amino acids at positionsshared by the compared sequences. Expression as a percentage ofhomology, similarity, or identity refers to a function of the number ofidentical or similar amino acids at positions shared by the comparedsequences. Various alignment algorithms and/or programs may be used todetermine percent identity or percent homology, including FASTA, BLAST,or ENTREZ. FASTA and BLAST are available as a part of the GCG sequenceanalysis package (University of Wisconsin, Madison, Wis.), and can beused with, e.g., default settings. ENTREZ is available through theNational Center for Biotechnology Information, National Library ofMedicine, National Institutes of Health, Bethesda, Md. In oneembodiment, the percent identity of two sequences can be determined bythe GCG program with a gap weight of 1, e.g., each amino acid gap isweighted as if it were a single amino acid or mismatch between the twosequences.

Conservative variation of amino acid residues entails the replacement ofone amino acid for another with like characteristics, or biologicallysimilar residue. For a detailed description of protein chemistry andstructure, see Schulz, G. E. et al., Principles of Protein Structure,Springer-Verlag, New York, 1979, and Creighton, T. E., Proteins:Structure and Molecular Principles, W. H. Freeman & Co., San Francisco,1984, which are hereby incorporated by reference. The types ofsubstitutions which may be made in the apelin peptides which areconservative substitutions are exemplified by exchanges within one ofthe following groups: 1. Small aliphatic, nonpolar or slightly polarresidues: e.g., Ala, Ser, Thr, Gly; 2. Polar, negatively chargedresidues and their amides: e.g., Asp, Asn, Glu, Gin; and 3. Polar,positively charged residues: e.g., His, Arg, Lys. 4. Hydrophobicresidues: e.g., lie, Val, Leu, Met. For example, the replacement of apolar residue for another, such as the substitution of arginine forlysine, glutamic for aspartic acids, or glutamine for asparagine; thereplacement of a hydrophobic residue such as isoleucine, valine, leucineor methionine for another, and the like. In a particular sequence, e.g.,aa2-aa3-aa4-aa5, a conservative variation means any one of more of theamino acids within the sequence can be replaced. As used herein“variant” and grammatical variations thereof, refers to a protein orpeptide that deviates from a reference protein or peptide sequence.Modified and variant proteins or peptides may therefore have greater orless activity or function than a reference protein or peptide but atleast retain partial activity or function of the reference protein orpeptide.

Most substitutions which are conservative are those which do not producesubstantial changes in the characteristics of the apelin peptide,although some changes disclosed herein are purposely designed to conferprolonged peptide stability in vitro and/or in vivo as explained herein.Even when it is difficult to predict the exact effect of a substitutionin advance of doing so, one skilled in the art will appreciate that theeffect can be evaluated by routine screening assays, including thebiological assays described herein. Modifications of apelin peptideproperties including redox or thermal stability, hydrophobicity,susceptibility to proteolytic degradation or the tendency to aggregatewith carriers or into multimers may be assayed by methods well known tothe ordinarily skilled artisan.

In some embodiments, the positions at amino acid 2 (aa2) and amino acid3 (aa3) of Formula (I) is Arg-Pro. In embodiments, the positions atamino acid 4 (aa4) and amino acid 5 (aa5) of Formula (I) is Arg-D-Leu.In embodiments, the positions at amino acid 4 (aa4) and amino acid 5(aa5) of Formula (I) is Arg-NMeLeu. In embodiments, the positions atamino acid 4 (aa4) and amino acid 5 (aa5) of Formula (I) is αMeArg-Leu.In embodiments, the positions at amino acid 4 (aa4) and amino acid 5(aa5) of Formula (I) is Arg-αMeLeu. In embodiments, the positions atamino acid 4 (aa4) and amino acid 5 (aa5) of Formula (I) is azaArg-Leu.In embodiments, the positions at amino acid 4 (aa4) and amino acid 5(aa5) of Formula (I) is Arg-azaLeu.

In some embodiments, the positions at amino acid 6 (aa′6) and amino acid7 (aa′7) of Formula (II) is Arg-Pro. In embodiments, the positions atamino acid 8 (aa′8) and amino acid 9 (aa′9) of Formula (II) isArg-D-Leu. In embodiments, the positions at amino acid 8 (aa′8) andamino acid 9 (aa′9) of Formula (II) is Arg-NMeLeu. In embodiments, thepositions at amino acid 8 (aa′8) and amino acid 9 (aa′9) of Formula (II)is αMeArg-Leu. In embodiments, the positions at amino acid 8 (aa′8) andamino acid 9 (aa′9) of Formula (II) is Arg-αMeLeu. In embodiments, thepositions at amino acid 8 (aa′8) and amino acid 9 (aa′9) of Formula (II)is azaArg-Leu. In embodiments, the positions at amino acid 8 (aa′8) andamino acid 9 (aa′9) of Formula (II) is Arg-azaLeu. In some embodiments,apelin peptides disclosed herein may be provided in a prodrug form. Theterm “prodrug” refers to a compound that is made more active (or simplyjust released) in vivo through metabolism of a precursor drug. Apelinpeptides can exist as prodrugs, as described in Hydrolysis in Drug andProdrug Metabolism: Chemistry, Biochemistry, and Enzymology (Testa,Bernard and Mayer, Joachim M. Wiley-VHCA, Zurich, Switzerland 2003).Prodrugs of the apelin peptides described herein are structurallymodified forms of the peptide that readily undergo chemical changesunder physiological conditions to provide the active apelin peptides.Additionally, prodrugs can be converted to the active peptide bychemical or biochemical methods in an ex vivo environment. For example,prodrugs can be slowly converted to an active peptide when placed in atransdermal patch reservoir with a suitable enzyme or chemical reagent.Prodrugs are often useful because, in some situations, they can beeasier to administer than the parent peptide. They may, for example,provide enhanced bioavailability by oral administration whereas theparent peptide may be unavailable through such administration routes.The prodrug can also have improved solubility in pharmaceuticalcompositions over the parent apelin peptide. A wide variety of prodrugderivatives are known in the art, such as those that rely on hydrolyticcleavage or oxidative activation of the prodrug. An example, withoutlimitation, of a prodrug would be an apelin peptide which isadministered as a C-terminal ester (the “prodrug”), but then ismetabolically hydrolyzed to the C-terminal carboxylic acid, the activeentity.

In some embodiments, the disclosure provides compositions containing theapelin peptides disclosed herein. In some embodiments, the compositionis a pharmaceutical composition. In certain embodiments, there areprovided pharmaceutical compostions containing apelin peptides for usein medicine.

In certain embodiments, apelin peptides disclosed herein may be providedas “pharmaceutically acceptable salts,” which may include salts orzwitterionic forms of the peptides which may be water or oil-soluble ordispersible and therapeutically acceptable. Pharmaceutically acceptablesalts can also be included therein, for example, hydrochloride,hydrobromide, phosphate, sulfate, maleate, fumarate, tartrates, acetate,propionate, malonate, benzoate, sulfonate, lactate, citrate, succinate,and the like. The salts can be prepared during the final isolation andpurification of the peptides or separately by adjusting the pH of theappropriate peptide formulation with a suitable acid or base. The term“pharmaceutically acceptable” means a biologically acceptableformulation, gaseous, liquid or solid, or mixture thereof, which issuitable for one or more routes of administration, in vivo delivery orcontact. A “pharmaceutically acceptable” composition is a material thatis not biologically or otherwise undesirable, e.g., the material may beadministered to a subject without causing substantial undesirablebiological effects. Thus, such a pharmaceutical composition may be used,for example, in administering an apelin peptide of the presentdisclosure to a subject.

Pharmaceutical compositions include solvents (aqueous or non-aqueous),solutions (aqueous or non-aqueous), emulsions (e.g., oil-in-water orwater-in-oil), suspensions, syrups, elixirs, dispersion and suspensionmedia, coatings, isotonic and absorption promoting or delaying agents,compatible with pharmaceutical administration or in vivo contact ordelivery. Aqueous and non-aqueous solvents, solutions and suspensionsmay include suspending agents and thickening agents. Suchpharmaceutically acceptable carriers include tablets (coated oruncoated), capsules (hard or soft), microbeads, powder, granules andcrystals. Supplementary active compounds (e.g., preservatives,antibacterial, antiviral and antifungal agents) can also be incorporatedinto the compositions.

Pharmaceutical compositions can be formulated to be compatible with aparticular route of administration or delivery known to one of skill inthe art. Thus, pharmaceutical compositions may include carriers,diluents, or excipients suitable for administration by various routes.Pharmaceutically acceptable excipients include, but are not limited to,liquids such as water, saline, glycerol, sugars and ethanol.Additionally, pharmaceutical compositions may also include auxiliarysubstances, such as wetting or emulsifying agents, pH bufferingsubstances, and the like.

Apelin peptide may be formulated for parenteral administration byinjection. Formulations for injection may be presented in unit dosageform, e.g., in ampoules or in multi-dose containers, with an addedpreservative. The compositions may take such forms as suspensions,solutions or emulsions in oily or aqueous vehicles, and may containformulatory agents such as suspending, stabilizing and/or dispersingagents. The formulations may be presented in unit-dose or multi-dosecontainers, for example sealed ampoules and vials, and may be stored inpowder form or in a freeze-dried (lyophilized) condition requiring onlythe addition of the sterile liquid carrier, for example, saline orsterile pyrogen-free water, immediately prior to use. Extemporaneousinjection solutions and suspensions may be prepared from sterilepowders, granules and tablets of the kind previously described.

Formulations for parenteral administration include aqueous andnon-aqueous (oily) sterile injection solutions of the active compoundswhich may contain antioxidants, buffers, bacteriostats and solutes whichrender the formulation isotonic with the blood of the intendedrecipient; and aqueous and non-aqueous sterile suspensions which mayinclude suspending agents and thickening agents. Suitable lipophilicsolvents or vehicles include fatty oils such as sesame oil, or syntheticfatty acid esters, such as ethyl oleate or triglycerides, or liposomes.Aqueous injection suspensions may contain substances which increase theviscosity of the suspension, such as sodium carboxymethyl cellulose,sorbitol, or dextran. Optionally, the suspension may also containsuitable stabilizers or agents which increase the solubility of thecompounds to allow for the preparation of highly concentrated solutions.

Apelin peptide may also be formulated for oral administration, such as,in the form of tablets, capsules.

In certain embodiments, the pharmaceutical composition may be formulatedto contain a concentration of at least about 0.01% w/w up to about 90%w/w or more of apelin peptide. Apelin peptides of the invention may beadministered orally or via injection at a therapeutically effectivedosage, such as a dose of from 0.01 to 500 mg/kg per day, from 1 to 400mg/kg per day, or from 2 to 300 mg/kg per day. The dose range for humansis generally from 5 mg to 2 g per day. The term “therapeuticallyeffective amount,” as used herein, when used in connection with treatinga subject is intended to qualify the amount of peptides used in thetreatment of a particular cardiovascular condition and/or prophylaxisagainst a particular cardiovascular condition. This amount will achievethe goal of preventing, reducing, or eliminating the damage ofmyocardial infarction, systemic hypertension, ischemic hear disease,abdominal aortic aneurysm, cardiac allograft vasculopathy, or the like.The therapeutically effective amount will vary depending upon thespecific activity of the therapeutic agent (i.e., peptidomimetic of thepresent disclosure) being used, the severity of the patient's diseasestate, and the age, physical condition, existence of other diseasestates, and nutritional status of the patient. Additionally, othermedication the patient may be receiving will effect the determination ofthe therapeutically effective amount of the therapeutic agent toadminister.

The unit dosage form may be provided in discrete units may convenientlycontain an amount of apelin peptide of the invention which is effectiveat such dosage or as a multiple of the same, for instance, unitscontaining 5 mg to 500 mg, usually around 10 mg to 200 mg.

A “unit dosage form,” as used herein, refers to physically discreteunits suited as unitary dosages for the subject to be treated; each unitcontaining a predetermined quantity optionally in association with apharmaceutical carrier (excipient, diluent, vehicle or filling agent)which, when administered in one or more doses, is calculated to producea desired effect (e.g., prophylactic or therapeutic effect). Unit dosageforms may be within, for example, ampules and vials, which may include aliquid composition, or a composition in a freeze-dried or lyophilizedstate; a sterile liquid carrier, for example, can be added prior toadministration or delivery in vivo.

Further, the apelin peptide of the invention may be administered on adaily basis or on a schedule containing days where dosing does not takeplace. In certain embodiments, dosing may take place every other day. Inother embodiments, dosing may take place for five consecutive days of aweek, then be followed by two non-dosing days. The choice of dosingschedule will depend on many factors, including, for example, theformulation chosen, route of administration, and concurrentpharmacotherapies, and may vary on a patient-to-patient basis. It isconsidered within the capacity of one skilled in the art to select aschedule that will maximize the therapeutic benefit and minimize anypotential side effects in a subject.

Compositions may be sterile. The compositions may be made in containerssuitable for such processes. Such containers include dishes, flasks,roller bottles, bags, bioreactors, vessels, tubes, vials, etc.Containers may be made of materials that include but are not limited toglass, plastic and polymers, such as polystyrene, polybutylene,polypropylene, etc.

Synthesis of Apelin Peptides

The apelin peptides of the present disclosure may be produced byconventional automated peptide synthesis methods. FIG. 3 shows thegeneral SPPS (solid phase peptide synthesis) approach for the divergentsyntheses of Arg/Leu modified apelin A2 peptides of the presentdisclosure.

Diagnostic and Prognostic Compositions

In some embodiments, the apelin peptides disclosed herein can be labeledfor detection and used, for example, to detect a binding site for thepeptide on the surface or in the interior of a cell. Thus, the fate ofthe peptide can be followed in vitro or in vivo by using the appropriatemethod to detect the label. The labeled apelin peptide may also beutilized in vivo for diagnosis and prognosis, or for other types of insitu evaluations.

Examples of suitable detectable labels include radioactive, fluorogenic,chromogenic, or other chemical labels. Useful radiolabels, which aredetected by a gamma counter or a scintillation counter or byautoradiography include 3H, 125I, 131I, 35S and 14C. In addition, 131Iis also useful as a therapeutic isotope (see below).

Common fluorescent labels include fluorescein isothiocyanate, rhodamine,phycoerythrin, phycocyanin, allophycocyanin, o-phthaldehyde andfluorescamine.

The fluorophore, such as the dansyl group, must be excited by light of aparticular wavelength to fluoresce. See, for example, Haugland, Handbookof Fluorescent Probes and Research Chemicals, Sixth Edition, MolecularProbes, Eugene, Oreg., 1996). In general, a fluorescent reagent isselected based on its ability to react readily with an amino function.Examples of such fluorescent probes include the Bodipy(4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) fluorophores which span thevisible spectrum (U.S. Pat. Nos. 4,774,339; 5,187,288; 5,248,782;5,274,113; 5,433,896; 5,451,663). One such member of this group is4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-propionicacid.

Fluorescein, fluorescein derivatives and fluorescein-like molecules suchas Oregon Green and its derivatives, Rhodamine Green and Rhodol Green,are coupled to amine groups using the isocyanate, succinimidyl ester ordichlorotriazinyl-reactive groups. The long wavelength rhodamines, whichare basically Rhodamine Green derivatives with substituents on thenitrogens, are among the most photostable fluorescent labeling reagentsknown. Their spectra are not affected by changes in pH between 4 and 10,an important advantage over the fluoresceins for many biologicalapplications. This group includes the tetramethylrhodamines,X-rhodamines and Texas Red derivatives. Other fluorophores forderivatizing the peptide are those which are excited by ultravioletlight. Examples include cascade blue, coumarin derivatives, naphthalenes(of which dansyl chloride is a member), pyrenes and pyridyloxazolederivatives.

In yet another approach, one or more amino groups is allowed to reactwith reagents that yield fluorescent products, for example,fluorescamine, dialdehydes such as o-phthaldialdehyde,naphthalene-2,3-dicarboxylate and anthracene-2,3-dicarboxylate.7-nitrobenz-2-oxa-1,3-diazole (NBD) derivatives, both chloride andfluoride, are useful to modify amines to yield fluorescent products.

Those skilled in the art will recognize that known fluorescent reagentsmodify groups other than amines, such as thiols, alcohols, aldehydes,ketones, carboxylic acids and amides. Hence, fluorescent substrates canreadily be designed and synthesized using these other reactive groups.

The peptide can also be labeled for detection usingfluorescence-emitting metals such as 152 Eu, or others of the lanthanideseries. These metals can be attached to the peptide using such metalchelating groups as diethylenetriaminepentaacetic acid (DTPA) orethylenediaminetetraacetic acid (EDTA). The peptide can be madedetectable by coupling it to a chemiluminescent compound. The presenceof the chemiluminescent-tagged peptide is then determined by detectingthe presence of luminescence that arises during the course of a chemicalreaction. Examples of particularly useful chemiluminescers are luminol,isoluminol, theromatic acridinium ester, imidazole, acridinium salt andoxalate ester. Likewise, a bioluminescent compound may be used to labelthe peptide. Bioluminescence is a type of chemiluminescence found inbiological systems in which a catalytic protein increases the efficiencyof the chemiluminescent reaction. The presence of a bioluminescentprotein is determined by detecting the presence of luminescence.Important bioluminescent compounds for purposes of labeling areluciferin, luciferase and aequorin.

In yet another embodiment, colorimetric detection is used, based onchromogenic compounds (chromophores) with high extinction coefficients.

In situ detection of the labeled peptide may be accomplished by removinga histological specimen from a subject and examining it by microscopyunder appropriate conditions to detect the label. Those of ordinaryskill will readily perceive that any of a wide variety of histologicalmethods (such as staining procedures) can be modified in order toachieve such in situ detection.

The term “diagnostically labeled” means that the peptide has attached toit a diagnostically detectable label. There are many different labelsand methods of labeling known to those of ordinary skill in the art.Examples of the types of labels which can be used in conjunction withapelin peptides include radioactive isotopes, paramagnetic isotopes, andcompounds which can be imaged by positron emission tomography (PET).Those of ordinary skill in the art will know of other suitable labelsfor binding to the apelin peptides disclosed herein, or will be able toascertain such, by routine experimentation. Furthermore, the binding ofthese labels to the peptide or derivative can be done using standardtechniques known to those of ordinary skill in the art.

For diagnostic in vivo radioimaging, the type of detection instrumentavailable is a major factor in selecting a given radionuclide. Theradionuclide chosen must have a type of decay which is detectable by agiven type of instrument. In general, any conventional method forvisualizing diagnostic imaging can be utilized in accordance withembodiments disclosed herein. Another factor in selecting a radionuclidefor in vivo diagnosis is that the half-life of a radionuclide be longenough so that it is still detectable at the time of maximum uptake bythe target issue, but short enough so that deleterious radiation of thehost is minimized. In one embodiment, a radionuclide used for in vivoimaging does not emit particles, but produces a large number of photonsin a 140-200 keV range, which may be readily detected by conventionalgamma cameras.

For in vivo diagnosis, radionuclides may be bound to peptide eitherdirectly or indirectly by using an intermediary functional group.Intermediary functional groups that are often used to bindradioisotopes, which exist as metallic ions, to peptides are thechelating agents, DTPA and EDTA. Examples of metallic ions which can bebound to peptides are 99Tc, 123I, 111In, 131I, 97Ru, 67Cu, 67Ga, 125I,68Ga, 72As, 89Zr, and 201Tl. Generally, the dosage of peptide labeledfor detection for diagnostic use will vary depending on considerationssuch as age, condition, sex, and extent of disease in the patient,counterindications, if any, and other variables, to be adjusted by theindividual physician.

In another embodiment, the apelin peptides disclosed herein may be usedas affinity ligands for binding the peptide's receptor in assays,preparative affinity chromatography or solid phase separation. Suchcompositions may also be used to enrich, purify or isolate cells towhich the peptide or derivative binds, preferably through a specificreceptor-ligand interaction. The peptide or derivative may beimmobilized using common methods known in the art, e.g. binding toCNBr-activated Sepharose or Agarose, NHS-Agarose or Sepharose,epoxy-activated Sepharose or Agarose, EAH-Sepharose or Agarose,streptavidin-Sepharose or Agarose in conjunction with biotinylatedpeptide or derivatives. In general the apelin peptides may beimmobilized by any other method which is capable of immobilizing thesecompounds to a solid phase for the indicated purposes. See, for exampleAffinity Chromatography: Principles and Methods (Pharmacia LKBBiotechnology). Thus, one embodiment is a composition comprising any ofthe peptides, derivatives or peptidomimetics described herein, bound toa solid support or a resin. The compound may be bound directly or via aspacer, such as an aliphatic chain having about 2-12 carbon atoms.

By “solid phase” or “solid support” or “carrier” is intended any supportor carrier capable of binding the peptide or derivative. Well-knownsupports, or carriers, in addition to Sepharose or Agarose describedabove are glass, polystyrene, polypropylene, polyethylene, dextran,nylon, amylases, natural and modified celluloses such as nitrocellulose,polyacrylamides, polyvinylidene difluoride, other agaroses, andmagnetite, including magnetic beads. The carrier can be totallyinsoluble or partially soluble. The support material may have anypossible structural configuration so long as the coupled molecule iscapable of binding to receptor material. Thus, the support configurationmay be spherical, as in a bead, or cylindrical, as in the inside surfaceof a test tube or microplate well, or the external surface of a rod.Alternatively, the surface may be flat such as a sheet, test strip,bottom surface of a microplate well, etc.

Production of Peptides and Derivatives

The peptides disclosed herein may be prepared using recombinant DNAtechnology. However, given their length, they may be more easilyprepared using solid-phase synthesis, such as that generally describedby Merrifield, J. Amer. Chem. Soc., 85:2149-54 (1963), although otherequivalent chemical syntheses known in the art are also useful.Solid-phase peptide synthesis may be initiated from the C-terminus ofthe peptide by coupling a protected alpha-amino acid to a suitableresin. Such a starting material can be prepared by attaching analpha-amino-protected amino acid by an ester linkage to achloromethylated resin or to a hydroxymethyl resin, or by an amide bondto a BHA resin or MBHA resin.

The preparation of the hydroxymethyl resin is described by Bodansky etal., 1966. Chloromethylated resins are commercially available fromBioRad Laboratories, Richmond, Calif. and from Lab. Systems, Inc. Thepreparation of such a resin is described by Stewart et al., 1969. BHAand MBHA resin supports are commercially available and are generallyused only when the desired polypeptide being synthesized has anunsubstituted amide at the C-terminus.

The amino acids can be coupled to the growing peptide chain usingtechniques well known in the art for the formation of peptide bonds. Forexample, one method involves converting the amino acid to a derivativethat will render the carboxyl group of the amino acid more susceptibleto reaction with the free N-terminal amino group of the growing peptidechain. Specifically, the C-terminal of the protected amino acid can beconverted to a mixed anhydride by the reaction of the C-terminal withethyl chloroformate, phenyl chloroformate, sec-butyl chloroformate,isobutyl chloroformate, or pivaloyl chloride or the like acid chlorides.Alternatively, the C-terminal of the amino acid can be converted to anactive ester, such as a 2,4,5-trichlorophenyl ester, a pentachlorophenylester, a pentafluorophenyl ester, a p-nitrophenyl ester, aN-hydroxysuccinimide ester, or an ester formed from1-hydroxybenzotriazole. Another coupling method involves the use of asuitable coupling agent, such as N,N′-dicyclohexylcarbodiimide orN,N′-diisopropylcarbodiimide. Other appropriate coupling agents,apparent to those skilled in the art, are disclosed in Gross et al.1979, which is hereby incorporated by reference.

The alpha-amino group of each amino acid employed in the peptidesynthesis must be protected during the coupling reaction to prevent sidereactions involving their active alpha-amino function. Certain aminoacids contain reactive side-chain functional groups (e.g., sulfhydryl,amino, carboxyl, and hydroxyl) and such functional groups must also beprotected with suitable protecting groups to prevent a chemical reactionfrom occurring at either (1) the alpha-amino group site or (2) areactive side chain site during both the initial and subsequent couplingsteps.

In the selection of a particular protecting group to be used insynthesizing the peptides, the following general rules are typicallyfollowed. Specifically, an alpha-amino protecting group (1) shouldrender the alpha-amino function inert under the conditions employed inthe coupling reaction, (2) should be readily removable after thecoupling reaction under conditions that will not remove side-chainprotecting groups and will not alter the structure of the peptidefragment, and (3) should substantially reduce the possibility ofracemization upon activation, immediately prior to coupling.

On the other hand, a side-chain protecting group (1) should render theside chain functional group inert under the conditions employed in thecoupling reaction, (2) should be stable under the conditions employed inremoving the alpha-amino protecting group, and (3) should be readilyremovable from the desired fully-assembled peptide under reactionconditions that will not alter the structure of the peptide chain.

It will be apparent to those skilled in the art that the protectinggroups known to be useful for peptide synthesis vary in reactivity withthe agents employed for their removal. For example, certain protectinggroups, such as triphenylmethyl and 2-(p-biphenyl)isopropyloxycarbonyl,are very labile and can be cleaved under mild acid conditions. Otherprotecting groups, such as t-butyloxycarbonyl (BOC), t-amyloxycarbonyl,adamantyl-oxycarbonyl, and p-methoxybenzyloxycarbonyl, are less labileand require moderately strong acids for their removal, such astrifluoroacetic, hydrochloric, or boron trifluoride in acetic acid.Still other protecting groups, such as benzyloxycarbonyl (CBZ or Z),halobenzyloxycarbonyl, p-nitrobenzyloxycarbonyl cycloalkyloxycarbonyl,and isopropyloxycarbonyl, are even less labile and require even strongeracids, such as hydrogen fluoride, hydrogen bromide, or borontrifluoroacetate in trifluoroacetic acid, for their removal. Suitableprotecting groups, known in the art are described in Gross et al. 1981.

Among the classes of amino acid protecting groups useful for protectingthe alpha-amino group or for protecting a side chain group are includedthe following:

(1) For an alpha-amino group, three typical classes of protecting groupsare: (a) aromatic urethane-type protecting groups, such asfluorenylmethyloxycarbonyl (FMOC), CBZ, and substituted CBZ, such as,p-chlorobenzyloxycarbonyl, p-nitrobenzyloxycarbonyl,p-bromobenzyloxycarbonyl, and p-methoxybenzyloxycarbonyl,o-chlorobenzyloxycarbonyl, 2,4-dichlorobenzyloxycarbonyl,2,6-dichlorobenzyloxycarbonyl, and the like; (b) aliphatic urethane-typeprotecting groups, such as BOC, t-amyloxycarbonyl, isopropyloxycarbonyl,2-(p-biphenyl)isopropyloxycarbonyl, allyloxycarbonyl and the like; and(c) cycloalkyl urethane-type protecting groups, such ascyclopentyloxycarbonyl, adamantyloxycarbonyl, and cyclohexyloxycarbonyl.The alpha-amino protecting groups BOC and FMOC are commonly used and mayprovide the widest selection for commericially available protected aminoacids.

(2) For the side chain amino group present in Lys, protection may be byany of the groups mentioned above in (1) such as BOC,2-chlorobenzyloxycarbonyl and the like.

(3) For the guanidino group of Arg, protection may be provided by nitro,tosyl, CBZ, adamantyloxycarbonyl,2,2,5,7,8-pentamethylchroman-6-sulfonyl,2,3,6-trimethyl-4-methoxyphenylsulfonyl, or BOC groups.

(4) For the hydroxyl group of Ser or Thr, protection may be, forexample, by t-butyl; benzyl (BZL); or substituted BZL, such asp-methoxybenzyl, p-nitrobenzyl, p-chlorobenzyl, o-chlorobenzyl, and2,6-dichlorobenzyl.

(5) For the carboxyl group of Asp or Glu, protection may be, forexample, by esterification using such groups as BZL, t-butyl,cyclohexyl, cyclopentyl, and the like.

(6) For the imidazole nitrogen of His, the benzyloxymethyl (BOM) ortosyl moiety is suitably employed as a protecting group.

(7) For the phenolic hydroxyl group of Tyr, a protecting group such astetrahydropyranyl, tert-butyl, trityl, BZL, chlorobenzyl, 4-bromobenzyl,and 2,6-dichlorobenzyl are suitably employed. One such protecting groupis bromobenzyloxycarbonyl.

(8) For the side chain amino group of Asn or Gin, xanthyl (Xan) may beemployed.

(9) For Met, the amino acid may be left unprotected.

(10) For the thio group of Cys, p-methoxybenzyl is typically employed.

The first C-terminal amino acid of the growing peptide chain istypically protected at the alpha-amino position by an appropriatelyselected protecting group such as BOC and the carboxyl residue attachedto a support, such as an amine functionalized support. Following thecoupling of the BOC-protected amino acid to the resin support, thealpha-amino protecting group is usually removed, typically by usingtrifluoroacetic acid (TFA) in methylene chloride or TFA alone. Thealpha-amino group de-protection reaction can occur over a wide range oftemperatures, but is usually carried out at a temperature between about0° C. and room temperature.

Other standard alpha-amino group de-protecting reagents, such as HCl indioxane, and conditions for the removal of specific alpha-aminoprotecting groups are within the skill of those working in the art, suchas those described in Lubke et al., 1975, which is hereby incorporatedby reference. Following the removal of the alpha-amino protecting group,the unprotected alpha-amino group, generally still side-chain protected,can be coupled in a stepwise manner in the intended sequence.

An alternative to the stepwise approach is the fragment condensationmethod in which pre-formed peptides of short length, each representingpart of the desired sequence, are coupled to a growing chain of aminoacids bound to a solid phase support. For this stepwise approach, aparticularly suitable coupling reagent is N,N′-dicyclohexylcarbodiimideor diisopropylcarbodiimide. Also, for the fragment approach, theselection of the coupling reagent, as well as the choice of thefragmentation pattern needed to couple fragments of the desired natureand size are important for success and are known to those skilled in theart.

Each protected amino acid or amino acid sequence is usually introducedinto the solid-phase reactor in amounts in excess of stoichiometricquantities, and the coupling is suitably carried out in an organicsolvent, such as dimethylformamide (DMF), CH₂Cl₂ or mixtures thereof. Ifincomplete coupling occurs, the coupling procedure is customarilyrepeated before removal of the N-amino protecting group in preparationfor coupling to the next amino acid. Following the removal of thealpha-amino protecting group, the remaining alpha-amino andside-chain-protected amino acids can be coupled in a stepwise manner inthe intended sequence. The success of the coupling reaction at eachstage of the synthesis may be monitored. A method of monitoring thesynthesis is by the ninhydrin reaction, as described by Kaiser et al.,1970. The coupling reactions can also be performed automatically usingwell-known commercial methods and devices, for example, a Beckman 990Peptide Synthesizer.

Upon completion of the desired peptide sequence, the protected peptidemay be cleaved from the resin support, and all protecting groupsremoved. The cleavage reaction and removal of the protecting groups maybe suitably accomplished concomitantly or consecutively withde-protection reactions. When the bond anchoring the peptide to theresin is an ester bond, it can be cleaved by any reagent that is capableof breaking an ester linkage and of penetrating the resin matrix. Oneespecially useful method is by treatment with liquid anhydrous hydrogenfluoride. This reagent will usually not only cleave the peptide from theresin, but will also remove all acid-labile protecting groups and, thus,will directly provide the fully de-protected peptide. When additionalprotecting groups that are not acid-labile are present, additionalde-protection steps must be carried out. These steps can be performedeither before or after the hydrogen fluoride treatment described above,according to specific needs and circumstances.

When a chloromethylated resin is used, the hydrogen fluoridecleavage/de-protection treatment generally results in the formation ofthe free peptide acids. When a benzhydrylamine resin is used, thehydrogen fluoride treatment generally results in the free peptideamides. Reaction with hydrogen fluoride in the presence of anisole anddimethylsulfide at 0° C. for one hour will typically remove theside-chain protecting groups and, concomitantly, release the peptidefrom the resin.

When it is desired to cleave the peptide without removing protectinggroups, the protected peptide-resin can be subjected to methanolysis,thus yielding a protected peptide in which the C-terminal carboxyl groupis methylated. This methyl ester can be subsequently hydrolyzed undermild alkaline conditions to give the free C-terminal carboxyl group. Theprotecting groups on the peptide chain can then be removed by treatmentwith a strong acid, such as liquid hydrogen fluoride. A particularlyuseful technique for methanolysis is that of Moore et al., 1977, inwhich the protected peptide-resin is treated with methanol and potassiumcyanide in the presence of a crown ether.

Other methods for cleaving a protected peptide from the resin when achloromethylated resin is employed include (1) ammoniolysis and (2)hydrazinolysis. If desired, the resulting C-terminal amide or hydrazidecan be hydrolyzed to the free C-terminal carboxyl moiety, and theprotecting groups can be removed conventionally. The protecting grouppresent on the N-terminal alpha-amino group may be removed eitherbefore, or after, the protected peptide is cleaved from the support.Purification of the apelin peptides disclosed herein may be achievedusing chromatographic techniques, such as preparative HPLC (includingreverse phase HPLC), gel permeation, ion exchange, partitionchromatography, affinity chromatography (including monoclonal antibodycolumns), and the like, or other conventional techniques such ascountercurrent distribution or the like.

An aspect of the present apelin peptides includes a method of treatingan apelin pathway disorder by administering the apelin peptide or apharmaceutical formulation thereof to a subject having the apelinpathway disorder.

The term “subject” refers to an animal, typically a mammal, such ashumans, non-human primates (apes, gibbons, gorillas, chimpanzees,orangutans, macaques), a domestic animal (dogs and cats), a farm animal(poultry such as chickens and ducks, horses, cows, goats, sheep, pigs),and experimental animals (mouse, rat, rabbit, guinea pig). Humansubjects include fetal, neonatal, infant, juvenile and adult subjects.

The term “apelin pathway disorder,” as used herein, refers to a disorderresulting from the abnormality of the apelin pathway. In someembodiments, the apelin pathway disorder is a cardiac disease, such as,but are not limited to, systemic arterial hypertension, systemichypertension, abdominal aortic aneurysm, pulmonary arterialhypertension, heart failure, myocardial ischemic-reperfusion injury,ischemic heart disease, cardiac allograft vasculopathy, myocardialinfarction, and high blood pressure.

Reducing Cardiac Reperfusion Injury Following Myocardial Infarction

In some embodiments, there are provided methods of reducing cardiacreperfusion injury following myocardial infarction in a subjectcomprising administering to the subject an effective amount of an apelinreceptor agonist comprising a peptidomimetic of Formula (I) or Formula(II) of the disclosure, or pharmaceutically acceptable salts thereof. Insome embodiments, the apelin peptide to prevent damage followingmyocardial infarction may be a peptidomimetic of Formula (I) or Formula(II) of the disclosure, or pharmaceutically acceptable salts thereof. Insome embodiments, combinations of apelin peptides may be employed. Insome embodiments, the administering step is carried out intravenously.

As used herein, the term “cardiac reperfusion injury” refers to aninjury of a heart, caused by putting the heart into an ischemiccondition such as by acute coronary syndromes, thomboembolic events,surgery or resuscitation from cardiac arrest.

As disclosed herein, APLN is a central regulator of the myocardialresponse to infarction and ischemia and pharmacologically targeting thispathway provides a means of developing new therapeutic agents. Apelin ispredominantly expressed in the endocardial and vascular endothelialcells while the APJ receptor (apelin receptor) is localized toendothelial and smooth muscle cells as well as cardiomyocytes, allowingfor autocrine and paracrine effects of apelin in the heart (Pitkin S.L., et al. Pharmacol. Rev. 62:331-342, (2010); Chen M. M., et al.Circulation. 108:1432-1439, (2003); Kleinz M J, et al. Regul Pept.126:233-240, (2005)). Apelin mediates positive inotropic effect onisolated cardiomyocytes (Wang C, et al. Am J Physiol Heart Circ Physiol.294:H2540-2546, (2008)), isolated perfused rat heart (Szokodi I, et al.Circ Res. 91:434-440, (2002)) and in vivo (Berry M F, et al.Circulation. 110:11187-193, (2004)) and mediates endothelium-dependentvasodilation (Pitkin S L et al. Br J Pharmacol. 160:1785-1795, (2010)).Genetic variation in the APJ receptor modifies the progression of heartfailure in patients with dilated cardiomyopathy (Sarzani R, et al. JCard Fail. 13:521-529, (2007)) and the apelin/APJ system is compromisedin human heart failure (Chen M. M., et al. Circulation. 108:1432-1439,(2003); Chong K S, et al. Eur J Heart Fail. 8:355-360, (2006)). Inpatients with chronic heart failure, apelin administration increasedcardiac index and lowered peripheral vascular resistance in the absenceof hypotension providing a promising new drug target for heart failure(Japp A G, et al. Circulation. 121:1818-1827, (2010)).

Apelin promotes the phosphorylation of Akt and increases theproliferation of endothelial cells in vitro indicating a pro-angiogenicrole (Kidoya H, et al. EMBO J. 27:522-534, (2008); Kidoya H, et al.Blood. 115:3166-3174, (2010); Tao J, et al. Am J Physiol Heart CircPhysiol. 301:H1471-1486, (2011)). Given the plethora of biochemical andcellular effects of apelin, it was postulated that loss of apelin mightenhance the susceptibility to myocardial ischemic injury. Apelinpeptides disclosed herein may prevent myocardial ischemic reperfusioninjury, which can be demonstrated using the Langendorff protocol(described in Example section). Apelin peptides disclosed herein mayrescue the heart from ischemic reperfusion injury compared to nativeisoforms (e.g., native isoform 2).

Tachycardia is directly correlated with native apelin isoforms bindingto the receptor. (Cheng, X., et al., European Journal of Pharmacology,470, 171-175 (2003)). Apelin peptides disclosed herein may demonstratean ability to induce tachycardia.

Modulating Vascular Tone and Blood Pressure

Native apelin peptides have been shown to play a central role invascular disease in other pathological states including pulmonaryhypertension (Alastalo, supra; Kim, J., et al. Nat. Med. 19:74-82(2013)) and diabetes (Sawane, M., et al. Diabetes 62:1970-80 (2013);Day, R. T., et al. Am. J. Physiol. Renal Physiol. 304:F788-800 (2013))It was indicated that a loss of apelin function is associated withworsening vascular disease with direct implications that apelin peptidescan reverse or prevent the progression of these disorders. Vascular tonerefers to the degree of constriction experienced by a blood vesselrelative to its maximally dilated state.

In some embodiments, there are provided methods of modulating vasculartone in a subject comprising administering to the subject an effectiveamount of an apelin receptor agonist comprising an apelin peptidecomprising a peptidomimetic of Formula (I) or Formula (II) of thedisclosure, or pharmaceutically acceptable salts thereof. In someembodiments, combinations of apelin peptides may be employed.

In some embodiments, there are provided methods of reducing bloodpressure in a subject comprising administering to the subject aneffective amount of an apelin receptor agonist comprising an apelinpeptide comprising a peptidomimetic of Formula (I) or Formula (II), orpharmaceutically acceptable salts thereof. In some embodiments, theadministering step is carried out intravenously.

Modulating Apelin Receptor

In some embodiments, there are provided methods of modulating an apelinpathway disorder comprising contacting the apelin receptor with anapelin peptide comprising a peptidomimetic of Formula (I) or Formula(II) of the disclosure, or pharmaceutically acceptable salts thereof. Insome embodiments, combinations of apelin peptides may be employed. Insome such emobdiments, the contacting step is performed in vivo. In somesuch embodiments, the apelin peptide is an apelin receptor agonist.

In some embodiments, there are provided methods of modulating an apelinpathway disorder in a subject comprising administering to the subject atherapeutically effective amount of an apelin peptide comprising apeptidomimetic of Formula (I) or Formula (II) of the disclosure, orpharmaceutically acceptable salts thereof. In some embodiments,combinations of apelin peptides may be employed. In some embodiments,the administering step is carried out intravenously.

Modulating apelin receptor may be useful in numerous biological contextswhere the receptor is expressed. In some embodiments, apelin peptidesdisclosed herein may be used to treat and/or reduce HIV-1 infection.Cayabyab et al., J. Virol. 74: 11972-11976 (2000) observed that inaddition to the chemokine receptors CCR5 and CXCR4, primary HIV-1isolates can also use APJ as a co-receptor. CAT reporter assays showedthat synthetic apelin peptides inhibited HIV-1 entry intoCD4-APJ-expressing cells.

As used herein, the singular forms “a”, “and,” and “the” include pluralreferents unless the context clearly indicates otherwise.

The following Examples are being submitted to illustrate embodiments ofthe present disclosure. Nevertheless, one skilled in the art, withoutdeparting from the spirit and scope of the invention, can make variouschanges and modifications of the invention to adapt it to various usagesand conditions. The following Examples are intended to be illustrativeonly and are not intended to limit the scope of the present disclosure.

EXAMPLES Reagents, Solvents and Purification

Commercially available chemical and biological reagents were purchasedfrom Sigma-Aldrich Canada, Chem-Impex International Inc., FisherScientific Ltd., Alfa Aesar Ltd., R&D Systems, Tocris Bioscience,Harvard Apparatus, Caledon or VWR International, and used withoutfurther purification unless otherwise stated. All solvents were ofAmerican Chemical Society (ACS) grade and were used without furtherpurification. All anhydrous reactions were conducted under positivepressure of argon using flame-dried glassware. Solvents for anhydrousreactions were distilled prior to use: dichloromethane anddichloroethane were distilled over calcium hydride, tetrahydrofuran anddiethyl ether were distilled over sodium with benzophenone as anindicator, and methanol was distilled over magnesium. HPLC gradeacetonitrile, dimethylformamide, 2-propanol, hexanes and methanol wereused without further purification. Commercially available ACS gradesolvents (>99.0% purity) were used for column chromatography withoutfurther purification. Deionized water was obtained from a Milli-Qreagent water filtration system (Millipore Co., Milford, Mass.). Theremoval of solvents in vacuo was performed by evaporation under reducedpressure using a Büchi rotary evaporator. Automated Solid Phase PeptideSynthesis was performed on a PreludeX (Gyros protein technologies). Allreactions and fractions from column chromatography were monitored bythin layer chromatography (TLC) using glass plates with a UV fluorescentindicator (normal SiO₂, Merck 60 F₂₅₄). Visualization was performedfollowing: UV absorption by fluorescence quenching, staining withphosphomolybdic acid in ethanol (10 g/100 mL), ninhydrin(ninhydrin:acetic acid:n-butanol, 0.6 g:6 mL:200 mL) or potassiumpermanganate (KMnO₄:K₂CO3:NaOH:H₂O, 1.5 g:10 g:0.12 g:200 mL). Flashchromatography was performed using Merck type 60, 230-400 mesh silicagel. Semi-preparative and analytical scale high performance liquidchromatography (HPLC) were performed on a Gilso393 chromatographequipped with model 322 pump heads, a model 171 diode array detector, aFC203B fraction collector and a Rheodyne 7725i injector fitted with a1000 pL sample loop. Columns used for purification were: Supelco Ascentis Si, C18 100 Å, 5 μm, 250 mm×4.6 mm; Restek Viva, BiPhenyl 300 Å,5 μm, 250 mm×4.6 mm; and Vydac BiPhenyl, 300 Å, 5 μm, 250 mm×4.6 mm.HPLC solvents were filtered through a Millipore filtration system undervacuum prior to use. Peptides were purified to >95% purity as assessedby analytical reinjection.

Characterization

Optical rotations were measured on a Perkin Elmer 241 polarimeter with amicrocell (10 cm, 1 mL) at ambient temperature and are reported in unitsof 10⁻¹ deg cm² g⁻¹. All reported optical rotations were referencedagainst air and measured at the sodium D line (λ=589.3 nm).

Infrared spectra (IR) were recorded on a Nicolet Magna 750 or a 20SXFT-IR spectrometer. Cast refers to the evaporation of a solution on aNaCl plate.

Nuclear magnetic resonance (NMR) spectra were recorded on anAgilent/Varian Inova 600, Inova 400, Inova 300, DD2 MR 400, VNMRS 700 orUnity 500 spectrometer at 27° C. For ¹H (300, 400, 500, 600. or 700 MHz)spectra, δ values were referenced to CDCl₃ (7.26 ppm), D₂O (4.79 ppm) orCD₃OD (3.30 ppm), and for ¹³C (100, 125, 150 or 175 MHz) spectra, δvalues were referenced to CDCl₃ (77.0 ppm) or CD₃OD (49.0 ppm), as thesolvents. Reported splitting patterns are abbreviated as s=singlet,d=doublet, t=triplet, q=quartet, sept=septet, m=multiplet.

Mass spectra (MS) were recorded on a Kratos AEIMS-50, Bruker 9.4TApex-Qe FTICR (high resolution, HRMS) or on a Perspective BiosystemsVoyager™ Elite MALDI-TOF MS using 4-hydroxy-α-cyanocinnamic acid (HCCA)as a matrix. MS/MS was performed on a Bruker UltraflextremeMALDI/TOF/TOF. LCMS was performed on an Agilent Technologies 6130 LCMSusing a Core-Shell C18 column (1.7 μm, 100 Å, Phenomenex Kintex).

General Apelin Peptide SPPS Elongation Method

A suspension of resin in DMF (10 mL) was bubbled under Ar gas for 15minutes to swell. The N-terminal Fmoc group was removed by bubbling asolution of 20% piperidine in DMF (3×10 mL) for 3 minutes, washingconsiderably with DMF (3×10 mL) after each deprotection.Fmoc-deprotection was monitored by TLC, with thedibenzofulvene-piperidine adduct appearing as aas a bright purple spotunder UV. To pre-activate the amino acid solution, one of the followingprocedures was followed: (1) DIPEA (2.2 eq) was added to a solution ofFmoc-protected amino acid (1.1 eq compared to resin loading), HOBt (1.1eq), and PyBOP (1.1 eq) in DMF (10 mL) and stirred for 5 minutes, or (2)DIPEA (6.0 equivalents) was added to a solution of Fmoc-protected aminoacid (3.0 equivalents compared to resin loading), HATU (3.0equivalents), and HOAt (1-hydroxy-7-azabenzotriazole) (3.0 equivalents)in DMF (10 mL) and stirred for 5 minutes. The activated amino acidsolution was added to the resin and bubbled under Ar gas for 1-3 h. Theresin was washed with DMF (3×10 mL) and the extent of coupling wasassessed by either: i) cleaving a small sample of resin with a solutionof 95:2.5:2.5 TFA:TIPS:H₂O for 1 h and MALDI-TOF analysis or ii)performing a Kaiser test to detect the presence of free amines. Asolution of 20% acetic anhydride in DMF (10 mL) was added to the resinand bubbled under Ar gas for 10 minutes to end-cap any unreacted amines.The resin was rinsed thoroughly with DMF (3×10 mL) and subjected toFmoc-deprotection to further elongate the peptide, or rinsed with CH₂Cl₂(3×10 mL) and MeOH (3×10 mL), dried thoroughly, and stored under Ar gasat −20° C.

General Method for Apelin Peptide Resin Cleavage

Resin-bound apelin peptide was suspended in 95:2.5:2.5 TFA:TIPS:H2O withshaking under an Ar atmosphere for 2-3 hours. The resin was removed viafiltration through glass wool, rinsed with TFA, and the solutionconcentrated in vacuo. Cold diethyl ether (1 mL, or 2×5 mL) was added totriturate the crude peptide. The diethyl ether and peptide precipitatewere decanted into a tube and centrifuged for 1 minute to pellet thepeptide. The diethyl ether was then decanted, and the pellet wasdissolved in 10% aqueous acetonitrile, 0.1% TFA.

Apelin Peptide Purification Methods

Peptides were purified using C18 RP-HPLC using aqueous 0.1% TFA (solventA) and 0.1% TFA in acetonitrile (solvent B) as eluents.

Example 1 Synthesis of D-Leu Peptides of pyr-1-apelin-13 A2 8 andApelin-17 A2 9

D-Substituted apelin A2 peptides were easily accessible due to thecommercial availability of Fmoc-protected D-amino acids. Following theFmoc-SPPS strategy outlined in FIG. 3, D-Leu peptides of pyr-1-apelin-13A2 8 and apelin-17 A2 9 were synthesized.

Example 2 Synthesis of Dipeptide 22 for the Preparation of α-MethylLeucine Apelin A2 Peptides 10 and 11

α-methylated Leu dipeptide 20 was synthesized through the HATU couplingof commercially available α-methyl-leucine benzyl ester p-TsOH salt withFmoc-Orn(Boc)-OH (Orn=ornithine) (FIG. 4). The ornithine 8-amine wasdeprotected under acidic conditions, and then guanidinylated with1,3-di-Boc-2-(trifluoromethylsulfonyl)guanidine to produce di-Bocprotected arginine dipeptide 21. Benzyl ester removal under Pd-catalyzedhydrogenolysis generated free acid 22, which was incorporated intoα-MeLeu apelin 13 and 17 A2 peptides 10 (SEQ ID NO:10) and 11 (SEQ IDNO:11) respectively.

Example 3 Synthesis of Dipeptide 29 for the Preparation of α-MethylLeucine Apelin A2 Peptides 12 and 13

The synthesis of dipeptide 29 is outlined in FIG. 5. Steric occlusion ofthe susceptible amide bond through α-methylation had previously beensuccessful in conferring resistance to ACE2 by the incorporation of AibN-terminal to the monocarboxypeptidase cleavage site. (Wang, W., et al.J. Am. Heart Assoc. 2, e000249 (2013)). Ni-Schiff base complex 23 wasused to enantioselectively prepare target α-methylated amino acids dueto: ease of synthesis; recyclability of the chiral ligand; and abilityto separate individual diastereomers by flash chromatographyAla-Ni(II)-(5)-BPB complex 23 was synthesized according to literatureprotocol (Belokon', Y. N., et al. Tetrahedron: Asymmetr: 9, 4249-4252(1998)) and was used to divergently synthesize both α-methyl arginineand α-methyl leucine amino acids.

For the synthesis of α-methyl arginine, 23 was deprotonated with KOtBuand alkylated with azido-3-iodopropane (24) to generateα,α-disubstituted Ni-complex 25. The desired (S,S)-diastereomer waspurified by silica flash chromatography in 69% yield, and the absolutestereochemistry was confirmed by X-ray crystallography (CCDC 1528624.Complex 25 was hydrolyzed under acidic conditions and the resultingamino acid was Fmoc-protected (26). A HATU-mediated peptide couplingwith H-Leu-OMe HCl salt afforded dipeptide 27, which was subsequentlyconverted to αMe-Arg containing dipeptide 28 through azidehydrogenolysis and guanidinylation. Methyl ester deprotection gave the

SPPS-compatible dipeptide 29 for the eventual preparation of αMeArgpeptides 12 and 13.

Example 4 Synthesis of Dipeptide 33 for the Preparation of α-MethylLeucine Apelin A2 Peptides 14 and 15

The synthesis of dipeptide 33 is outlined in FIG. 6. To prepare α-methylleucine, 23 was alkylated with 2-methyl-1-iodopropane to generate thedesired (S,5)-diastereomer 30, with the absolute stereochemistryconfirmed by X-ray crystallography. Acid hydrolysis followed byFmoc-protection produced amino acid 31, which was subsequently coupledto H-Ser(tBu)-OMe to give dipeptide 32. Methyl ester deprotection gavethe SPPS-compatible dipeptide 33, which was used for αMeLeu apelinpeptides 14 and 15.

Example 5 Synthesis of Azatripeptide 39 for the Preparation ofAza-Arginine Apelin A2 Peptides 16 and 17

The synthesis of dipeptide 39 is outlined in FIG. 7. Azadipeptide 34 wasprepared by the sequential addition of disuccinimidyl carbonate, then asolution of H-Leu-OtBu in DIPEA (N,N-diisopropylethylamine) tobenzophenone hydrazone analogous to previously established literatureprotocol. (Traore, M., et al., Org. Lett. 16, 3588-3591 (2014),Garcia-Ramos, Y., et al., J. Pept. Sci. 19, 725-729 (2013)).Regioselective semicarbazone alkylation was achieved withtetraethylammonium hydroxide and 3-chloro-1-bromopropane to yieldchloroalkylated product 35. Displacement of the primary alkyl chloridewith sodium azide afforded 36, which was deprotected to semicarbazide 37with hydroxylamine hydrochloride. Semicarbazide 37 was aminoacylatedwith the next N-terminal amino acid (Fmoc-Pro-OH) to generateazatripeptide 38. The SPPS compatible tripeptide 39 was synthesizedfollowing tert-butyl ester deprotection, hydrogenolysis of the azide,and guanidinylation of the primary amine. Tripeptide 39 was incorporatedinto azaArg apelin peptides 16 and 17.

Example 6 Synthesis of Azatripeptide 45 for the Preparation ofAza-Leucine Apelin A2 Peptides 18 and 19

The synthesis of dipeptide 45 is outlined in FIG. 8. To prepare asynthetic azaLeu tripeptide, 40 was prepared by the sequential additionof disuccinimidyl carbonate, then a solution of H-Ser(tBu)-OtBu in DIPEAto benzophenone hydrazone. Semicarbazone alkylation was accomplishedusing tetraethylammonium hydroxide and 3-bromo-2-methylpropene to yield41. Concomitant Pd-catalyzed hydrogenation and hydrogenolysis affordedsemicarbazide 42, which was coupled to Fmoc-Orn(2-Cl-Cbz)-OH to generateazatripeptide 43. Chemoselective tert-butyl ester deprotection to freeacid 44 was accomplished by addition of silica in refluxing toluene toprotected azatripeptide 43. Subsequent 2-chloro-Cbz deprotection andguanidinylation of the resultant primary amine yielded azatripeptide 45,which was further employed to generate azaLeu-containing peptides 18 and19.

Example 7 Synthesis and Characterization of Apelin Peptides

Compounds 23 and 24

Compounds 23 and 24 were prepared according to literature protocolsdescribed in the literatures. See, Tetrahedron: Asymmetry, 9, 4249-4252(1998); WO 2011047215.

Fmoc-pBrPhe-2-Cl-Trt (6)

2-Chlorotrityl chloride resin (1.05 mmol) was transferred to a SPPSvessel, washed with CH₂Cl₂ (2×10 mL), DMF (2×10 mL), and finallysuspended in DMF and bubbled under Ar gas for 10 minutes.Fmoc-p-bromo-L-phenylalanine (1.0 mmol) was suspended in dry CH₂Cl₂ (10mL) with DIPEA (5.0 equivalents) and added to the swollen resin. Thissolution was bubbled under Ar gas for 2.5 h. The functionalized resinwas washed considerably with CH₂Cl₂ (3×10 mL) and DMF (3×10 mL), andthen unreacted sites were capped by bubbling with dry MeOH (5 mL) underAr gas for 45 minutes. The resin was dried thoroughly under Ar, weighedand divided into 0.2 mmol portions, and stored under an Ar atmosphere at−20° C. “Trt” refers to trityl.

Fmoc-His(Trt)-Lys(Boc)-Gly-Pro-Nle-Aib-pBrPhe-2-Q-Trt (7)

Functionalized resin 6 was elongated by manual SPPS, introducing aminoacids in the following order: Fmoc-Aib-OH, Fmoc-Nle-OH, Fmoc-Pro-OH,Fmoc-Gly-OH, Fmoc-Lys(Boc)-OH, and Fmoc-His(Trt)-OH. A small sample ofthe resin was cleaved and analysed by MALDI-TOF: Calculated forC₅₃H₆₈BrN₁₀O₁₀ 1083.4, found 1083.0 (M+H)+.

Synthesis of D-Leu Substituted A2 Peptides

D-Leu5-pyr-1-apelin-13 A2 (8)

Advanced intermediate 7 (0.1 mmol) was subjected to manual SPPS,introducing amino acids in the following order: Fmoc-Ser(tBu)-OH,Fmoc-D-Leu-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Pro-OH, Fmoc-Arg(Pmc)-OH, andpyr-Glu-OH. A portion (0.05 mmol) of resin-bound peptide was cleaved andpurified using a C₁₈ RP-HPLC analytical column (Method A), eluting at20.6 min. The desired peptide was isolated as a white solid afterlyophilization (11.3 mg, 14%). Monoisotopic MW calculated forC₆₉H₁₁₁BrN₂₂O₁₆ 791.3860, found high resolution (FTICR-ESI-MS) 791.3846(M+2H)²⁺.

D-Leu9-apelin-17 A2 (9)

Advanced intermediate 7 (0.1 mmol) was subjected to manual SPPS,introducing amino acids in the following order: Fmoc-Ser(tBu)-OH,Fmoc-D-Leu-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Pro-OH, Fmoc-Arg(Pmc)-OH,Fmoc-Gln(Trt)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Phe-OH, andFmoc-Lys(Boc)-OH. A portion (0.05 mmol) of resin-bound peptide wascleaved and purified using a C₁₈ RP-HPLC analytical column (Method A),eluting at 11.2 min. The desired peptide was isolated as a white solidafter lyophilization (9.9 mg, 9.1%). Monoisotopic MW calculated forC₉₆H₁₆₁BrN3₄O₂₀ 547.2947, found high resolution (FTICR-ESI-MS) 547.2942(M+4H)⁴⁺.

Synthesis of α-Methyl Leucine A2 Peptides BenzylA-((5,)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-5-((tert-butoxycarbonyl)amino) pentanoyl)-A-methyl-L-leucinate (20)

Fmoc-Orn(Boc)-OH (1.23 g, 2.70 mmol), HATU (1.03 g, 2.70 mmol), HOAt(4.5 mL [0.6 M solution in DMF], 2.70 mmol), and DIPEA (1.28 mL, 7.36mmol) were dissolved in dry DMF (10 mL) and stirred for 5 minutes topreactivate the amino acid. A solution of N-Me-Leu-OBn p-TsOH(para-toluenesulfonic acid) salt (1.00 g, 2.45 mmol) and DIPEA (0.43 mL,2.45 mmol) in dry CH₂Cl₂ (10 mL) was added and the reaction was stirredfor 17 h at room temperature. The reaction was washed with 10% aqueousNaHCO₃ (20 mL), 10% aqueous citric acid (20 mL) and brine (20 mL). Theorganic layer was dried over Na₂SO₄, filtered, and concentrated invacuo. The dipeptide was purified using flash chromatography (silicagel, 25% EtOAc in hexanes), obtaining 20 as a crunchy white solid (1.25g, 76%). (R_(f) 0.9 on SiO₂, 1:3 hexanes:EtOAc); [α]_(D) ²⁶ 500-17.4 (c1.0 CH₂Cl₂); IR (CH₂Cl₂ cast) 3315, 3066, 3037, 2957, 2870, 1714, 1645,1513, 1451, 1251, 1172 cm⁻¹; ¹H (CDCl₃, 500 MHz): δ 7.76 (d, J=7.5 Hz,2H, Ar—H), 7.59 (d, J=7.5 Hz, 2H, Ar—H), 503 7.43-7.27 (m, 9H, Ar—H),5.65 (d, J=8.5 Hz, 1H, Fmoc-NH), 5.35 (dd, J=10.8, 5.0 Hz, 1H, Leu-CHα),5.19-5.06 (m, 2H, Bn-OCH2504), 4.68 (ddd, J=7.7, 7.7, 4.8 Hz, 1H,Orn-CHα), 4.51 (s, 1H, Boc-NH), 4.37 (ddd, J=10.6, 7.1, 7.1 Hz, 2H,Fmoc-CH₂), 4.21 (t, J=7.1 Hz, 1H, Fmoc-CH), 3.09-3.04 (m, 2H, Orn-CH₂δ),2.93 (s, 3H, N—CH₃), 1.81-1.65 (m, 3H, 2×Leu-CH₂β, Orn-CH₂β), 1.56-1.46(m, 4H, Orn-CH₂β, 2×Orn-CH₂γ, 507 Leu-CH(CH₃)₂), 1.44 (s, 9H, —C(CH₃)₃),1.01-0.84 (m, 6H, —CH(CH₃)₂); ¹³C (CDCl3508, 125 MHz): δ 172.6, 171.3,156.0, 155.9, 143.9, 143.8, 141.3, 141.3, 135.4, 128.7, 128.5, 128.4,127.7, 127.1, 127.1, 125.2, 120.0, 79.1, 510 67.1, 67.0, 54.9, 50.7,47.2, 40.1, 36.8, 31.1, 30.0, 28.5, 25.4, 24.9, 23.2, 21.4; HRMS (ES)Calculated for C₃₉H₅₀N₃O₇ 672.3643, found 672.3642 (M+H)⁺ 511.

Benzyl(11S,14S,E)-11-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-6-((tert-butoxycarbonyl)amino)-14-isobutyl-2,2,13-trimethyl-4,12-dioxo-3-oxa-5,7,13-triazapentadec-5-en-15-oate(21)

The guanidinylation reaction was adapted from a literature procedure.⁵⁸TFA (5 mL) was added to a solution of dipeptide 20 (0.701 g, 1.04 mmol)in dry CH₂Cl₂ (10 mL) and stirred for 1 h. The reaction was concentratedin vacuo, using diethyl ether co-evaporations to remove residual TFA.The yellow oil was resuspended in dry CH₂Cl₂ (20 mL) and1,3-di-Boc-2-(trifluoromethylsulfonyl)guanidine (0.449 g, 1.15 mmol) andtriethylamine (0.32 mL, 2.30 mmol) were added and stirred for 80minutes. The reaction was washed with 2 N aqueous sodium bisulfate (10mL) and 10% NaHCO₃ (10 mL), dried over Na₂SO₄, filtered, andconcentrated in vacuo. The dipeptide was purified using flashchromatography (silica gel, 20% EtOAc in hexanes), obtaining 21 as acrunchy white solid (0.820 g, 97%). (R 0.5 on SiO₂, 3:1 hexanes:EtOAc);[α]_(D) ²⁶ −12.5 (c 1.21 CHCl₃); IR (CHCl₃ cast) 3331, 2959, 2871, 1721,1640, 1451, 1415, 1330, 1156, 1134 cm⁻¹; ¹H (CDCl₃, 500 MHz): δ 8.29 (t,J=5.4 Hz, 1H, Arg-NHε), 7.76 (d, J=7.6 Hz, 2H, Ar—H), 7.60 (d, J=7.6 Hz,2H, Ar—H), 7.43-7.27 (m, 9H, Ar—H), 5.68 (d, J=8.5 Hz, 1H, Fmoc-NH),5.37-5.28 (m, 1H, Leu-CHα), 5.23-5.05 (m, 2H, —OCH ₂Ph), 4.67 (td,J=8.1, 4.3 Hz, 1H, Arg-CHα), 4.44-4.31 (m, 2H, Fmoc-CH ₂), 4.21 (t,J=6.9 Hz, 1H, Fmoc-CH), 3.36 (ddd, J=7.4, 5.0, 3.2 Hz, 2H, Arg-CH ₂δ),2.93 (s, 3H, N—CH ₃), 1.82-1.75 (m, 1H, Leu-CH ₂β), 1.75-1.66 (m, 2H,Leu-CH ₂β, Arg-CH ₂β), 1.63-1.55 (m, 3H, Arg-CH ₂β, 2×Arg-CH ₂γ) 1.49(m, 10H, Leu-CH(CH₃)₂, —C(CH ₃)₃), 1.48 (s, 9H, —C(CH ₃)₃), 0.93 (d,J=6.6 Hz, 3H, Leu-CH(CH ₃)₂), 0.90 (d, J=6.5 Hz, 3H, Leu-CH(CH ₃)₂); ¹³C(CDCl₃, 125 MHz): δ 172.5, 171.2, 163.6, 156.2, 156.0, 153.3, 143.9,143.8, 141.3, 141.3, 135.4, 128.7, 128.6, 128.4, 127.7, 127.1, 127.1,125.2, 125.2, 120.0, 83.1, 79.2, 67.1, 67.0, 54.9, 50.8, 47.2, 40.3,36.8, 31.2, 29.9, 28.3, 28.1, 27.9, 27.9, 24.9, 23.2, 21.4; HRMS (ES)Calculated for C₄₅H₆₀N₅O₉ 814.4386, found 814.4378 (M+H)⁺.

(11S,14S,E)-11-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-6-((tert-butoxycarbonyl)amino)-14-isobutyl-2,2,13-trimethyl-4,12-dioxo-3-oxa-5,7,13-triazapentadec-5-en-15-oicAcid (22)

A solution of 21 (0.501 g, 0.62 mmol) was dissolved in methanol (50 mL)and had 10% Pd/C (20 mg) added. The suspension was stirred underhydrogen gas for 22 h, filtered through a pad of Celite, andconcentrated in vacuo. The crude residue was purified using flashchromatography (silica gel, 5% MeOH in CH₂Cl₂, 0.1% AcOH), yielding 22as a white solid (0.378 g, 85%). (R_(f) 0.2 on SiO₂, 1% AcOH in EtOAc);[α]_(D) ²⁶ −2.8 (c 1.0 CH₂Cl₂); IR (CH₂Cl₂ cast) 3326, 3140, 3066, 2959,2872, 1721, 1641, 1618, 1451, 1415, 1331, 1253, 1136 cm⁻¹; ¹H (CDCl₃,500 MHz):

δ 8.48 (s, 1H, Arg-NHε), 7.76 (d, J=7.5 Hz, 2H, Ar—H), 7.61 (d, J=7.5Hz, 2H, Ar—H), 7.40 (t, J=7.5 Hz, 2H, Ar—H), 7.32 (tdd, J=7.5, 3.4, 1.2Hz, 2H, Ar—H), 6.05 (d, J=7.6 Hz, 1H, Fmoc-N—H), 5.37 (dd, J=10.7, 5.1Hz, 1H, Leu-CHα), 4.80 (dd, J=5.4, 5.3 Hz, 1H, Arg-CHα), 4.38 (dd,J=10.6, 7.2 Hz, 2H, Fmoc-CH ₂), 4.21 (t, J=7.1 Hz, 1H, Fmoc-CH),3.55-3.45 (m, 1H, Arg-CH ₂δ), 3.14-3.05 (m, 1H, Arg-CH ₂δ), 2.98 (s, 3H,N—CH ₃), 1.92-1.56 (m, 6H, 2×Leu-CH ₂β, 2×Arg-CH ₂β, 2×Arg-CH ₂γ), 1.52(s, 9H, —C(CH ₃)₃), 1.49 (m, 10H, Leu-CH(CH ₃)₂, —C(CH ₃)₃), 0.96 (d,J=6.6 Hz, 3H, Leu-CH(CH ₃)₂), 0.93 (d, J=6.5 Hz, 3H, Leu-CH(CH ₃)₂); ¹³C(CDCl₃, 125 MHz): δ 172.3, 172.1, 162.8, 156.3, 155.7, 153.2, 144.9,143.8, 141.4, 141.3, 127.7, 127.7, 127.1, 127.1, 125.2, 125.2, 120.0,119.9, 83.1, 80.6, 66.9, 54.7, 51.1, 47.3, 40.6, 36.1, 30.7, 28.4, 28.1,28.1, 24.8, 23.2, 21.4; HRMS (ES) Calculated for C₃₈H₅₄N₅O₉ 724.3916,found 724.3924 (M+H)⁺.

N-MeLeu5-pyr-1-apelm-13 A2 (10)

Advanced intermediate 7 (0.1 mmol) was subjected to manual SPPS,introducing amino acids in the following order: Fmoc-Ser(tBu)-OH, 22,Fmoc-Pro-OH, Fmoc-Arg(Pmc)-OH. The resin was split into half, andFmoc-SPPS was continued on 0.1 mmol scale, coupling pyr-Glu-OH. Noendcapping was performed following addition of 22. A portion (0.05 mmol)of resin-bound peptide was cleaved as previously described and purifiedusing a C₁₈ RP-HPLC analytical column (Method A), eluting at 11.2 min.The desired peptide was isolated as a white solid after lyophilization(6.0 mg, 7%). Monoisotopic MW calculated for C₇₀H₁₁₄BrN₂₂O₁₆ 532.5983,found high resolution (FTICR-ESI-MS) 532.5972 (M+3H)³⁺.

N-MeLeu9-apelin-17 A2 (11)

The remaining 0.1 mmol carried over from the synthesis of 10 was coupledwith: Fmoc-Gln(Trt)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Phe-OH,and Fmoc-Lys(Boc)-OH. No endcapping was performed following addition of22. A portion (0.05 mmol) of resin-bound peptide was cleaved aspreviously described and purified using a C₁₈ RP-HPLC analytical column(Method A), eluting at 11.3 min. The desired peptide was isolated as awhite solid after lyophilization (23.8 mg, 22%). Monoisotopic MWcalculated for C₉₇H₁₆₃BrN₃₄O₂₀ 550.7986, found high resolution(FTICR-ESI-MS) 550.7983 (M+4H)⁴⁺.

Synthesis of α-Methyl Arginine A2 Peptides 1-azido-3-iodopropane (24)

Compound 24 was prepared according to literature procedures.⁴³ Asolution of 1-chloro-3-iodopropane (2.63 mL, 24.5 mmol) and sodium azide(1.91 g, 29.4 mmol) in dry DMF (60 mL) was stirred at room temperaturefor 24 h. The reaction was diluted by the addition of water (100 mL) anddiethyl ether washes (2×100 mL) were used to extract organic components.The diethyl ether fractions were dried over Na₂SO₄, filtered andconcentrated in vacuo until a small volume (˜10 mL) of ether remained.The reaction was diluted in acetone (60 mL) and following the additionof sodium iodide (5.50 g, 36.7 mmol), the reaction was heated at 60° C.for 24 h. The solution was concentrated in vacuo until a small volume(˜10 mL) remained, then diluted with diethyl ether (100 mL) and washedwith H₂O (2×100 mL). The organic layer was dried over Na₂SO₄, vacuumfiltered through a small plug of alumina, and concentrated in vacuo,obtaining the desired product as a light yellow oil (3.91 g, 76%). IR(CH₂Cl₂ cast) 2927, 2869, 2098, 1449, 1428, 1347, 1290, 1224, 1173 cm⁻¹;¹H (CDCl₃, 500 MHz): δ3.44 (t, J=6.4 Hz, 2H, —CH₂N₃), 3.25 (t, J=6.6 Hz,2H, —CH₂I), 2.04 (app pentet, J=6.5 Hz, 2H, —CH₂—); ¹³C (CDCl₃, 125MHz): δ 51.5, 32.4, 2.3.

(2S)-2-(3′-azidopropyl)-2-methyl-glycine-Ni(II)-(S)-BPB (25)

Complex 25 was prepared according to literature procedure.⁴³ Nickelcomplex 23 (6.49 g, 12.7 mmol) and potassium tert-butoxide (2.13 g, 19.0mmol) were added to an RBF and dissolved in dry DMF (50 mL) at 0° C.under an Ar atmosphere. This solution was stirred for 3 minutes,followed by the addition of a solution of 24 (5.01 g, 19.0 mmol) in dryDMF (10 mL). The reaction was stirred at 0° C. for 45 minutes, thenwarmed to room temperature for 75 minutes. 5% aqueous acetic acid (200mL) was added to quench the reaction, followed by extraction withCH₂Cl₁₂ (3×75 mL). Pooled organic layers were washed with brine (2×75mL), dried over Na₂SO₄, filtered and concentrated in vacuo. The desireddiastereomer was purified by flash chromatography (silica gel; 2.5% MeOHin EtOAc), yielding 25 as a red solid (5.18 g, 69%). Crystals of 25 wereobtained after dissolution in minimal CH₂Cl₂, dilution with hexanes andslow evaporation. (R_(f)0.6 on SiO₂, 9:1 EtOAc:MeOH); [α]_(D) ²⁶ 1853.4(c 1.0 CH₂Cl₂); IR (CH₂Cl₂ cast) 3060, 2937, 2869, 2097, 1673, 1639,1574, 1439, 1359, 1253, 1165 cm⁻¹;

¹H (CDCl₃, 500 MHz): δ 8.12-8.07 (m, 2H, Ar—H ₁), 8.05 (dd, J=8.7, 0.9Hz, 1H, Ar—H ₄), 7.55-7.48 (m, 2H, Ar—H ₈, Ar—H ₉), 7.47-7.41 (m, 3H,Ar—H ₂, Ar—H ₁₁), 7.35-7.28 (m, 2H, ArH₃, Ar—H ₁₀), 7.16 (ddd, J=8.5,5.8, 2.7 Hz, 1H, Ar—H ₅), 7.08 (dt, J=7.6, 1.3 Hz, 1H Ar—H ₁₂),6.69-6.62(m, 2H, Ar—H ₆, Ar—H₇),4.50 (d, J=12.7 Hz, 1H, Ph-CH ₂—N), 3.70 (dd,J=18.7, 11.8 Hz, 2H, Ph-CH ₂—N, Pro-CH ₂δ), 3.51-3.42 (m, 2H, Pro-CHα,—CH₂N₃), 3.32-3.20 (m, 2H, —CH ₂N₃, Pro-CH ₂γ), 2.71 (dddd, J=12.8, 7.1,5.8, 2.6 Hz, 1H, Pro-CH ₂β, 2.58-2.43 (m, 2H, Pro-CH ₂β, —CH ₂CH₂N₃),2.26-2.04 (m, 3H, —CH ₂CH₂N₃, Pro-CH ₂γ, Pro-CH ₂δ, 1.86 (ddd, J=13.8,12.4, 4.2 Hz, 1H, —CH₂CH₂CH₂N₃), 1.76 (ddd, J=13.7, 12.4, 4.6 Hz, 1H,—CH ₂CH₂CH₂N₃), 1.28 (s, 3H, —CH ₃); ¹³C (CDCl₃, 125 MHz): δ 182.0,180.6, 172.8, 141.6, 136.4, 133.4, 133.4, 131.8, 131.7, 130.2, 129.6,129.1, 129.0, 128.5, 128.1, 127.3, 127.1, 124.0, 120.8, 77.4, 70.0,63.5, 57.2, 51.3, 37.5, 30.7, 29.4, 25.5, 23.4; HRMS (ES) Calculated forC₃₁H₃₂N₆NaNiO₃ 617.1782, found 617.1785 (M+Na)⁺.

(S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-5-azido-2-methylpentanoicAcid (26)

A solution of 3N HCl:MeOH (1:1, 40 mL) was heated to 70° C. and had 25(2.60 g, 4.37 mmol) dissolved in MeOH (10 mL) added dropwise over 5minutes. The reaction mixture was stirred for 50 minutes at 70° C.,turning from dark red to green as the reaction proceeded. The reactionwas cooled to room temperature, concentrated in vacuo and resuspended in10% aqueous sodium carbonate (20 mL). EDTA disodium salt (3.25 g, 8.73mmol) was added and stirred for 0.5 h at room temperature. The reactionwas cooled to 0° C. and had a solution of Fmoc-OSu (1.62 g, 4.80 mmol)dissolved in acetone (20 mL) added to it. This reaction was slowlywarmed to room temperature and stirred for 16 h. The following day, thereaction was diluted with EtOAc (50 mL) and washed with 1 N HCl (3×20mL). The organic layer was dried over MgSO₄, filtered, and concentratedin vacuo. The product was purified by flash chromatography (silica gel,1-5% MeOH in CH₂Cl₂ gradient), yielding 26 as a white solid (1.64 g,95%). (R_(f)0.4 on SiO₂, 9:1 EtOAc:MeOH); ¹H (CDCl₃, 500 MHz): δ 7.77(d, J=7.5 Hz, 2H, Ar—H), 7.58 (d, J=7.5 Hz, 2H, Ar—H), 7.40 (td, J=7.4,3.1 Hz, 2H, Ar—H), 7.32 (tdd, J=7.4, 2.6, 1.1 Hz, 2H, Ar—H), 5.57 (br s,1H, Fmoc-NH), 4.48-4.36 (m, 2H, Fmoc-CH ₂), 4.21 (t, J=6.2 Hz, 1H,Fmoc-CH), 3.32-3.19 (m, 2H, —CH ₂N₃), 2.28-2.17 (m, 1H, Orn-CH ₂γ),2.02-1.90 (m, 1H, Orn-CH ₂γ), 1.60 (br s, 3H, —CH ₃), 1.50-1.39 (m, 2H,Orn-CH ₂β); ¹³C (CDCl₃, 125 MHz): δ 170.1, 153.9, 143.8, 141.4, 127.7,127.1, 125.0, 120.0, 66.6, 51.1, 47.2, 34.0, 33.4, 23.7, 23.5; HRMS (ES)Calculated for C₂₁H₂₁N₄O₄ 393.1568, found 393.1566 (M−H)⁻.

Methyl((S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-5-azido-2-methyl-pentanoyl)-L-leucinate(27)

Compound 26 (1.61 g, 4.09 mmol), HATU (1.55 g, 4.09 mmol), HOAt (0.68 mL[0.6 M solution in DMF], 0.41 mmol), and DIPEA (2.85 mL, 16.4 mmol) weredissolved in dry DMF (25 mL) and stirred for 5 minutes to preactivatethe amino acid. A solution of H-Leu-OMe*HCl (0.780 g, 4.29 mmol) in dryCH₂Cl₂ (25 mL) was added and the reaction was stirred for 16 h at roomtemperature. The reaction was concentrated in vacuo, resuspended inEtOAc (50 mL), and washed with 10% citric acid, water, and brine (50mL). The organic layer was dried over Na₂SO₄, filtered, and concentratedin vacuo. Crude 27 was purified using flash chromatography (silica gel,33% EtOAc in hexanes), obtaining the desired dipeptide as a yellow oil(1.22 g, 57%). (R_(f) 0.5 on SiO₂, 2:1 hexane:EtOAc); [α]_(D) ²⁶ −1.2 (c1.0 CHCl₃); IR (CHCl₃ cast) 3342, 2956, 2872, 2097, 1731, 1664, 1495,1450, 1249, 1089 cm⁻¹; ¹H(CDCl₃, 500 MHz): δ7.76 (dd, J=7.4, 1.0 Hz, 2H,Ar—H), 7.59 (ddd, J=7.5, 4.0, 1.0 Hz, 2H, Ar—H), 7.44-7.35 (m, 2H,Ar—H), 7.32 (dddd, J=7.5, 7.5, 2.2, 1.2 Hz, 2H, Ar—H), 6.38 (br s, 1H,Leu-NH), 5.83 (br s, 1H, Fmoc-NH), 4.60 (ddd, J=8.6, 8.0, 4.7 Hz, 1H,Leu-CHα), 4.49-4.35 (m, 2H, Fmoc-CH ₂), 4.20 (t, J=6.6 Hz, 1H, Fmoc-CH),3.72 (s, 3H, —OCH ₃), 3.34-3.18 (m, 2H, Arg-CH ₂δ), 2.47-2.23 (m, 1H,Arg-CH ₂β), 1.84-1.76 (m, 1H, Arg-CH ₂β), 1.70-1.40 (m, 8H, Arg-CH ₃,2×Arg-CH₂γ, 2×Leu-CH₂β, —CH(CH₃)₂), 0.93 (m, 6H, —CH(CH ₃)₂); ¹³C(CDCl₃, 125 MHz): δ 173.4, 173.1, 154.6, 143.9, 143.9, 141.4, 127.7,127.1, 127.1, 125.0, 120.0, 66.5, 59.4, 52.4, 51.2, 51.1, 47.3, 41.3,33.9, 25.0, 24.0, 23.5, 22.8, 21.9; HRMS (ES) Calculated forC₂₈H₃₅N₅NaO₅ 544.2530, found 544.2527 (M+Na)+.

Methyl((S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-5-((Z)-2,3-bis(tert-butoxycarbonyl)guanidino)-2-methylpentanoyl)-L-leucinate(28)

The guanidinylation reaction was adapted from a literature procedure.⁵⁸Dipeptide 27 (1.16 g, 2.23 mmol) was dissolved in MeOH (50 mL) and had10% Pd/C (20 mg) added. The suspension was stirred under hydrogen gasfor 2 h, filtered through a pad of Celite, and concentrated in vacuo.The crude residue was suspended in CH₂Cl₂ (30 mL) and1,3-di-Boc-2-(trifluoromethylsulfonyl)guanidine (0.961 g, 2.45 mmol) andtriethylamine (0.69 mL, 4.91 mmol) were added. This reaction was stirredat room temperature under Ar for 18 h, concentrated in vacuo, andpurified using flash chromatography (silica gel, 35% EtOAc in hexanes),yielding 28 as a white solid (1.08 g, 66%). (R_(f)0.4 on SiO₂, 3:1hexane:EtOAc); [α]_(D) ²⁶ 3.2 (c 1.0 CHCl₃); IR (CHCl₃ cast) 3332, 2959,1723, 1644, 1619, 1495, 1451, 1369, 1332, 1234, 1155, 1135, 1057 cm⁻¹;¹H (CDCl₃, 500 MHz): δ 8.28 (s, 1H, Arg-NH _(ε)), 7.76 (dt, J=7.5, 0.9Hz, 2H, Ar—H), 7.60 (ddq, J=7.7, 5.0, 1.0 Hz, 2H, Ar—H), 7.46-7.36 (m,2H, Ar—H), 7.32 (dddd, J=7.4, 7.4, 3.8, 1.2 Hz, 2H, Ar—H), 6.39 (br s,1H, Leu-NH), 5.82 (br s, 1H, Fmoc-NH), 4.62-4.53 (m, 1H, Leu-CHα),4.46-4.36 (m, 2H, Fmoc-CH ₂), 4.21 (t, J=6.7 Hz, 1H, FmocCH ₂), 3.71 (s,3H, —OCH ₃), 3.44-3.32 (m, 2H, Arg-CH ₂δ), 2.35-2.19 (m, 1H, Arg-CH ₂β),1.82-1.71 (m, 1H, Arg-CH ₂β), 1.70-1.51 (m, 8H, Arg-CH ₃, 2×Arg-CH ₂γ,2×Leu-CH ₂β, —CH(CH₃)₂), 1.49 (s, 9H, —C(CH ₃)₃), 1.48 (s, 9H, —C(CH₃)₃), 0.93 (d, J=6.2 Hz, 6H, —CH(CH ₃)₂); ¹³C (CDCl₃, 125 MHz): δ 173.5,173.2, 163.5, 156.2, 153.2, 143.9, 143.9, 141.3, 127.7, 127.1, 127.1,125.0, 120.0, 83.1, 79.3, 66.5, 59.5, 52.4, 51.1, 47.3, 41.2, 40.6,28.3, 28.1, 25.0, 24.0, 23.7, 22.8, 21.8; HRMS (ES) Calculated forC₃₉H₅₆N₅O₉ 738.4073, found 738.4069 (M+H)⁺.

((S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-5-((Z)-2,3-bis(tert-butoxy-carbonyl)guanidino)-2-methylpentanoyl)-L-leucine(29)

Methyl ester deprotection conditions were adapted from a literatureprotocol.⁴⁴ Dipeptide 28 (1.06 g, 1.44 mmol) was dissolved in aqueous2-propanol (70% 2-propanol in water, 50 mL) and had CaCl₂.2H₂O (5.88 g)added to generate a 0.8 M Ca²⁺ solution. Sodium hydroxide (0.115 g, 2.87mmol) was added and the reaction was stirred for 3.5 h. Acetic acid(0.164 mL, 2.87 mmol) was added to neutralize residual base, and thereaction was concentrated in vacuo. The crude residue was dissolved inminimal MeOH and the dipeptide was precipitated by the addition of H₂Oand collected by vacuum filtration, yielding 29 as a white solid (0.982g, 94%). (R_(f)0.05 on SiO₂, 1:1 hexane:EtOAc); [α]_(D) ²⁶ −6.0 (c 1.0MeOH); IR (MeOH cast) 3347, 2957, 1722, 1641, 1450, 1416, 1368, 1331,1135 cm⁻¹; ¹H (CD₃OD, 500 MHz): δ 7.89 (s, 1H, Arg-NH _(ε)), 7.78 (dt,J=7.6, 0.9 Hz, 2H, Ar—H), 7.70-7.64 (m, 2H, Ar—H), 7.41-7.34 (m, 2H,Ar—H), 7.30 (td, J=7.4, 1.1 Hz, 3H, Ar—H), 4.38 (d, J=6.6 Hz, 2H,Fmoc-CH ₂), 4.25-4.19 (m, 2H, Fmoc-CH, LeuCHα), 3.33-3.27 (m, 2H, Arg-CH₂δ), 2.03-1.94 (m, 1H, Arg-CH ₂β), 1.84-1.75 (m, 1H, Arg-CH ₂β),1.68-1.52 (m, 4H, —CH(CH₃)₂, 2×Leu-CH ₂β, Arg-CH ₂γ), 1.50 (d, J=3.7 Hz,10H, —C(CH ₃)₃, Arg-CH ₂γ), 1.44 (s, 9H, —C(CH ₃)₃), 1.40 (s, 3H, Arg-CH₃), 0.88 (d, J=6.4 Hz, 3H, —CH(CH ₃)₂, 0.87 (d, J=6.4 Hz, 3H, —CH(CH₃)₂; ¹³C (CDCl₃, 125 MHz): δ 176.3, 172.4, 164.6, 157.5, 154.1, 145.3,142.7, 128.9, 128.2, 126.2, 121.0, 84.5, 80.4, 79.5, 67.8, 60.6, 49.6,49.3, 41.8, 28.6, 28.3, 26.1, 24.7, 23.7, 22.1; HRMS (ES) Calculated forC₃₈H₅₄N₅O₉ 724.3916, found 724.3913 (M+H)+.

α-MeArg4-pyr-1-apelin-13 A2 (12)

Advanced intermediate 7 (0.2 mmol) was subjected to manual SPPS (solidphase peptide synthesis), introducing amino acids in the followingorder: Fmoc-Ser(tBu)-OH, 29, Fmoc-Pro-OH, Fmoc-Arg(Pmc)-OH. The resinwas split into half, and Fmoc-SPPS was continued on 0.1 mmol scale,coupling pyr-Glu-OH. No endcapping was performed following addition of29. A portion (0.05 mmol) of resin-bound peptide was cleaved aspreviously described and purified using a C₁₈ RP-HPLC analytical column(Method A), eluting at 13.4 min. The desired peptide was isolated as awhite solid after lyophilization (8.5 mg, 11%). Monoisotopic MWcalculated for C₇₀H₁₁₄BrN₂₂O₁₆ 532.5983, found high resolution(FTICR-ESI-MS) 532.5973 (M+3H)³⁺.

α-MeArc8-apelin-17 A2 (13)

The remaining 0.1 mmol carried over from the synthesis of 12 was coupledwith: FmocGln(Trt)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Phe-OH,and Fmoc-Lys(Boc)-OH. No endcapping was performed following addition of29. A portion (0.05 mmol) of resin-bound peptide was cleaved aspreviously described and purified using a C₁₈ RP-HPLC analytical column(Method A), eluting at 13.0 min. The desired peptide was isolated as awhite solid after lyophilization (12.5 mg, 11%). Monoisotopic MWcalculated for C₉₇H₁₆₃BrN₃₄O₂₀ 550.7986, found high resolution(FTICR-ESI-MS) 550.7974 (M+4H)⁴⁺.

Synthesis of α-Methyl Leucine A2 Peptides(2S)-2-(2′-methylpropyl)-2-methyl-glycine-Ni(II)-(S)-BPB (30)

Alkylation conditions were adapted from literature protocol.⁴² Nickelcomplex 23 (3.20 g, 6.25 mmol) and potassium tert-butoxide (1.05 g, 9.37mmol) were added to an RBF and dissolved in dry DMF (25 mL) at 0° C.under an Ar atmosphere. This solution was stirred for 3 minutes,followed by the addition of 1-iodo-2-methylpropane (2.16 mL, 18.7 mmol).The reaction was stirred at 0° C. for 30 minutes, then warmed to roomtemperature for an additional 75 minutes. 5% aqueous acetic acid (100mL) was added to quench the reaction, followed by extraction with CH₂Cl₂(3×75 mL). The pooled organic layers were washed with brine (2×75 mL),dried over Na₂SO₄, filtered and concentrated in vacuo. The desireddiastereomer was purified by flash chromatography (silica gel; 2.5% MeOHin EtOAc), yielding 30 as a red solid (2.43 g, 69%). Crystals of 30 wereobtained after dissolution in minimal CH₂Cl₂, dilution with hexanes andslowevaporation. (R_(f) 0.6 on SiO₂, 9:1 EtOAc:MeOH); [α]_(D) ²⁶ 1683.7(c 1.0 CHCl₃); IR (CHCl₃ cast) 2959, 2870, 1668, 1639, 1535, 1439, 1360,1253, 1170 cm⁻¹;

¹H (CDCl₃, 500 MHz): δ 8.12-8.06 (m, 3H Ar—H₁, Ar—H₄), 7.51-7.43 (m, 2H,Ar—H₈, Ar—H₉), 7.42-7.36 (m, 3H, Ar—H₂, Ar—H₁₁), 7.34-7.22 (m, 2H,Ar—H₃, Ar—H₁₀), 7.12 (ddd, J=8.6, 6.7, 1.9 Hz, 1H, Ar—H₅), 7.06-7.00 (m,1H, Ar—H₁₂), 6.64-6.53 (m, 2H, Ar—H₆, Ar—H₇), 4.48 (d, J=12.7 Hz, 1H,Ph-CH₂—N), 3.74-3.64 (m, 2H, Ph-CH₂—N, Pro-CH₂δ), 3.45 (dd, J=10.6, 6.1Hz, 1H, Pro-CHα), 3.26-3.10 (m, 1H, Pro-CH₂γ), 2.74-2.65 (m, 1H,Pro-CH₂β), 2.56-2.37 (m, 2H, Pro-CH₂β, Leu-CHy), 2.13-2.00 (m, 2H,Pro-CH₂γ, Pro-CH₂δ), 1.73-1.60 (m, 2H, Leu-CH₂β), 1.27 (d, J=6.6 Hz, 3H,Leu-CH₃δ), 1.22 (s, 3H, Leu-CH₃β), 1.14 (d, J=6.7 Hz, 3H, Leu-CH₃δ); ¹³C(CDCl₃, 125 MHz): δ 182.9, 180.6, 172.3, 141.7, 136.8, 133.6, 133.5,131.7, 131.6, 130.5, 129.4, 129.0, 128.9, 128.4, 127.8, 126.9, 123.8,120.6, 77.5, 70.2, 63.6, 57.1, 48.5, 30.7, 30.7, 25.6, 24.5, 23.3, 23.3;HRMS (ES) Calculated for C₃₂H₃₆N₃NiO₃ 568.2105, found 568.2100 (M+H)⁺.

(S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-2,4-dimethylpentanoicAcid (31)

A solution of 3N HCl:MeOH (1:1, 10 mL) was heated to 70° C. and had 30(2.36 g, 4.16 mmol) dissolved in MeOH (5 mL) added dropwise over 5minutes. The reaction mixture was stirred for 40 minutes, turning fromdark red to green as the reaction proceeded. The reaction was cooled toroom temperature, concentrated in vacuo and resuspended in 10% aqueoussodium carbonate (25 mL). EDTA disodium salt (3.09 g, 8.31 mmol) wasadded and stirred for 0.5 h at room temperature. The reaction was cooledto 0° C. and had a solution of Fmoc-OSu (1.54 g, 4.57 mmol) dissolved inacetone (25 mL) added to it. This reaction was slowly warmed to roomtemperature and stirred for 22 h. The following day, the reaction wasdiluted with EtOAc (50 mL) and washed with 1 N HCl (3×50 mL). Theorganic layer was dried over MgSO₄, filtered, and concentrated in vacuo.The product was purified by flash chromatography (silica gel, 1-5% MeOHin CH₂Cl₂ gradient), yielding 31 as a white solid (1.45 g, 95%).(R_(f)0.35 on SiO₂, 7.5% MeOH in CH₂Cl₁₂); ¹H (CDCl₃, 500 MHz): δ7.80-7.74 (m, 2H, Ar—H), 7.64-7.57 (m, 2H, ArH), 7.43-7.38 (m, 2H,Ar—H), 7.37-7.29 (m, 2H, Ar—H), 5.92 (br s, 1H, N—H), 4.46-4.33 (m, 2H,Fmoc-CH ₂), 4.32 (t, 1H, J=6.0 Hz Fmoc-CH), 2.26-2.19 (m, 1H, Leu-CH₂β), 1.83-1.73 (m, 1H, Leu-CH ₂β), 1.70-1.55 (m, 4H, Leu-CHγ, Leu-CH₃β), 0.96-0.82 (m, 6H, 2×LeuCH₃δ); ¹³C (CDCl₃, 125 MHz): δ 179.4, 155.2,143.9, 141.6, 127.8, 127.1, 124.8, 120.0, 65.1, 47.3, 24.9, 24.7, 23.8,23.0; HRMS (ES) Calculated for C₂₂H₂₄NO₄ 366.1711, found 366.1706(M−H)⁻.

MethylN—((S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-2,4-dimethyl-pentanoyl)-O-(tert-butyl)-L-serinate(32)

Amino acid 31 (1.53 g, 4.16 mmol), HATU (1.58 g, 4.16 mmol), HOAt (0.69mL [0.6 M solution in DMF], 0.42 mmol), and DIPEA (2.90 mL, 16.6 mmol)were dissolved in dry DMF (25 mL) and stirred for 5 minutes topreactivate the amino acid. A solution of H-Ser(tBu)-OMe.HCl (0.925 g,4.37 mmol) in dry CH₂Cl₂ (25 mL) was added and the reaction was stirredfor 20 h at room temperature. The reaction was concentrated in vacuo,resuspended in EtOAc (50 mL), and washed with 10% citric acid, water,and brine (50 mL). The organic layer was dried over Na₂SO₄, filtered,and concentrated in vacuo. Crude 32 was purified using flashchromatography (silica gel, 25% EtOAc in hexanes), obtaining the desiredproduct as a whitesolid (0.872 g, 40%). (Rf 0.2 on SiO₂, 3:1hexanes:EtOAc); [α]_(D) ²⁶ 20.4 (c 1.0 CHCl3); IR (CHCl₃ cast) 3440,3384, 2973, 2956, 2872, 1730, 1669, 1493, 1364, 1241, 1099 cm⁻¹; ₁H(CDCl₃, 500 MHz): δ 7.76 (dd, J=7.6, 0.9 Hz, 2H, Ar—H), 7.64-7.58 (m,2H, Ar—H), 7.39 (ddd, J=6.8, 6.8, 0.8 Hz, 2H, Ar—H), 7.31 (ddd, J=7.4,6.8, 1.1 Hz, 2H, Ar—H), 6.64 (br s, 1H, SerNH), 6.09 (s, 1H, Fmoc-NH),4.74-4.68 (m, 1H, Ser-CHα), 4.43-4.30 (m, 2H, Fmoc-CH ₂), 4.22 (t, J=6.8Hz, 1H, Fmoc-CH), 3.81 (d, J=8.8 Hz, 1H, Ser-CH ₂β), 3.75 (s, 3H, —OCH₃), 3.57 (d, J=8.8 Hz, 1H, Ser-CH ₂β), 2.44-2.31 (m, 1H, Leu-CH ₂β),1.73-1.52 (m, 5H, LeuCH ₂β, Leu-CHγ, Leu-CH3β), 1.13 (s, 9H, —C(CH ₃)₃),0.94-0.82 (m, 6H, 2×Leu-CH ₃δ); ¹³C (CDCl₃, 125 MHz): δ 173.9, 170.7,154.4, 144.1, 144.0, 141.3, 127.6, 127.1, 125.1, 120.0, 73.4, 66.4,61.9, 59.6, 53.1, 52.4, 47.3, 45.1, 27.3, 25.2, 24.7, 23.7, 23.6; HRMS(ES) Calculated for C₃₀H₄₁N₂O₆ 525.2959, found 525.2956 (M+H)+.

N—((S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-2,4-dimethylpentanoyl)-O-(tert-butyl)-L-serine(33)

Methyl ester deprotection conditions were adapted from literatureprocedure.⁴⁴ Dipeptide 32 (0.853 g, 1.63 mmol) was dissolved in aqueous2-propanol (70% 2-propanol in water, 50 mL) and had CaCl₂.2H₂O (5.88 g)added to generate a 0.8 M Ca²⁺ solution. Sodium hydroxide (0.130 g, 3.25mmol) was added and the reaction was stirred for 4 h. Acetic acid (0.186mL, 3.25 mmol) was added to neutralize residual base, and the reactionwas concentrated in vacuo. The crude residue purified by flashchromatography (silica gel, 50% EtOAc in hexanes 0.1% AcOH), yieldingdipeptide 33 as a white sticky solid (0.368 g, 44%). (R_(f) 0.3 on SiO₂,0.1% AcOH in EtOAc); [α]_(D) ²⁶ 27.0 (c 1.0 CHCl₃); IR (CHCl₃ cast)3386, 3320, 3068, 3018, 2974, 2876, 1727, 1665, 1497, 1450, 1240, 1194,1105 cm⁻¹; ¹H (CDCl₃, 500 MHz): δ 7.76 (dd, J=7.7, 0.9 Hz, 2H, Ar—H),7.59 (ddd, J=7.5, 2.0, 1.0 Hz, 2H, Ar—H), 7.40 (ddd, J=7.5, 7.5, 0.9 Hz,2H, Ar—H), 7.31 (ddd, J=7.7, 7.5, 1.2, Hz, 2H, Ar—H), 6.78 (br s, 1H,Ser-NH), 5.73 (s, 1H, Fmoc-NH), 4.67-4.56 (m, 1H, Ser-CHα), 4.48-4.34(m, 2H, Fmoc-CH ₂), 4.20 (t, J=6.6 Hz, 1H, Fmoc-CH), 3.95-3.88 (m, 1H,Ser-CH ₂β, 3.54-3.48 (m, 1H, Ser-CH ₂β, 2.19-2.07 (m, 1H, Leu-CH ₂β,1.72-1.59 (m, 2H, Leu-CH ₂β, Leu-CHγ), 1.54 (s, 3H, Leu-CH ₃β), 1.19 (s,9H, —C(CH ₃)₃), 0.94-0.82 (m, 6H, 2×Leu-CH ₃δ); ¹³C (CDCl₃, 125 MHz): δ174.3, 172.0, 154.9, 143.8, 141.4, 129.1, 128.2, 127.7, 127.1, 125.0,120.0, 74.7, 66.6, 61.0, 59.9, 52.7, 47.2, 45.8, 27.7, 24.4, 24.0, 23.6;HRMS (ES) Calculated for C₂₉H₃₇N₂O₆ 509.2657, found 509.2657 (M−H)⁻.

α-MeLeu5-pyr-1-apelin-13 A2 (14)

Advanced intermediate 7 (0.2 mmol) was subjected to manual SPPS,introducing amino acids in the following order: 33, Fmoc-Pro-OH, andFmoc-Arg(Pmc)-OH. The resin was split into half, and Fmoc-SPPS wascontinued on 0.1 mmol scale, coupling pyr-Glu-OH. No endcapping wasperformed following addition of 33. A portion (0.05 mmol) of resin-boundpeptide was cleaved as previously described and purified using a C₁₈RP-HPLC analytical column (Method A), eluting at 13.7 min. The desiredpeptide was isolated as a white solid after lyophilization (8.5 mg,11%). Monoisotopic MW calculated for C₇₀H₁₁₄BrN₂₂O₁₆ 532.5983, foundhigh resolution (FTICR-ESI-MS) 532.5972 (M+3H)³⁺. “Pmc” refers to2,2,5,7,8-pentamethylchroman-6-sulfonyl.

α-MeLeu9-apelin-17 A2 (15)

The remaining 0.1 mmol carried over from the synthesis of 14 was coupledwith FmocGln(Trt)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Phe-OH,and Fmoc-Lys(Boc) OH. A portion (0.05 mmol) of resin-bound peptide wascleaved as previously described and purified using a C₁₈ RP-HPLCanalytical column (Method A), eluting at 11.5 min. The desired peptidewas isolated as a white solid after lyophilization (14.3 mg, 13%).Monoisotopic MW calculated for C₉₇H₁₆₃BrN₃₄O₂₀ 550.7986, found highresolution (FTICR-ESI-MS) 550.7974 (M+4H)⁴⁺.

Synthesis of Aza-Arginine A2 Peptides Tert-Butyl(2-(diphenylmethylene)hydrazine-1-carbonyl)-L-leucinate (34)

Semicarbazone 34 was prepared by modifying a literature procedure.₄₆ Asolution of benzophenone hydrazone (4.39 g, 22.4 mmol) in dry CH₂Cl₂ (50mL) was cooled to 0° C. and cannulated into a 0° C. solution ofdisuccinimidyl carbonate (7.41 g [85% purity], 24.6 mmol) in dry CH₂Cl₂(50 mL) and dry DMF (10 mL). The reaction was warmed to room temperaturefor 45 minutes, then cooled down to 0° C. A 0° C. solution ofH-Leu-OtBu.HCl (5.00 g, 22.4 mmol) and DIPEA (7.79 mL, 44.7 mmol) in dryCH₂Cl₂ (50 mL) was then cannulated into the reaction vessel and allowedto slowly come up to room temperature over 16 h. The reaction wasconcentrated in vacuo and purified by flash chromatography (silica gel,20% EtOAc in hexanes), yielding a light yellow sticky solid (8.29 g,91%). (R_(f) 0.8 on SiO₂, 1:1 hexanes:EtOAc); [α]_(D) ²⁶ 36.7 (c 1.27CHCl₃); IR (CHCl₃ cast) 3414, 3355, 3188, 3062, 2957, 2871, 1732, 1682,1519, 1446, 1368, 1153, 1113 cm⁻¹; ¹H (CDCl₃, 400 MHz): δ 7.59 (s, 1H,═N—NH), 7.57-7.46 (m, 5H, Ar—H), 7.40-7.29 (m, 3H, Ar—H), 7.29-7.22 (m,2H, Ar—H), 6.68 (d, J=9.0 Hz, 1H, Leu-NH), 4.52 (ddd, J=8.8, 8.8, 5.6Hz, 1H, Leu-CHα), 1.85-1.74 (m, 1H, Leu-CHγ), 1.74-1.60 (m, 2H, Leu-CH₂β), 1.50 (s, 9H, —C(CH ₃)₃), 1.00 (d, J=6.5 Hz, 6H, 2×Leu-CH ₃δ); ¹³C(CDCl₃, 125 MHz): δ 172.6, 154.9, 148.2, 137.0, 131.9, 129.8, 129.7,129.4, 129.3, 128.8, 128.5, 128.3, 128.1, 127.2, 126.5, 81.7, 51.9,42.4, 28.1, 25.0, 23.0, 22.1; HRMS (ES) Calculated for C₂₄H₃₂N₃O₃410.2438, found 410.2438 (M+H)⁺.

Tert-Butyl(1-(3-chloropropyl)-2-(diphenylmethylene)hydrazine-1-carbonyl)-L-leucinate(35)

Alkylation conditions were initially adapted from a literatureprocedure.⁴⁵ Semicarbazone 34 (2.47 g, 6.03 mmol) was dissolved in THF(50 mL) and cooled to 0° C. Aqueous tetraethylammonium hydroxide (22.2mL [20% solution], 30.1 mmol) was added and stirred for 30 minutes,followed by the addition of 1-bromo-3-chloropropane (4.47 mL, 45.2 mmol)at 0° C. The reaction was slowly warmed to room temperature and wasquenched after 72 h by the addition of 10% citric acid (20 mL) followedby brine (20 mL). Organic components were extracted with EtOAc (3×100mL), dried over Na₂SO₄, filtered and concentrated in vacuo. Alkylatedsemicarbazone 204 was purified by flash chromatography (silica gel, 15%EtOAc in hexanes) and was isolated as a yellow oil (2.16 g, 74%). (Rf0.85 on SiO₂, 2:1 hexanes:EtOAc); [α]_(D) ²⁶ 67.5 (c 1.42 CHCl₃); IR(CHCl₃ cast) 3414, 3061, 2959, 2870, 1734, 1682, 1499, 1446, 1368, 1154cm⁻¹; ¹H (CDCl₃, 500 MHz): δ 7.55-7.41 (m, 6H, Ar—H), 7.41-7.30 (m, 4H,Ar—H), 6.69 (d, J=8.7 Hz, 1H, Leu-NH), 4.47 (ddd, J=8.8, 8.7, 5.6 Hz,1H, Leu-CHα), 3.46 (dt, J=14.7, 6.8 Hz, 1H, N—CH ₂), 3.38-3.27 (m, 3H,N—CH ₂, 2×N—CH₂CH ₂), 1.80-1.72 (m, 3H, 2×-CH ₂Cl, Leu-CHγ), 1.66 (ddd,J=13.6, 8.0, 5.6 Hz, 1H, Leu-CH ₂β), 1.61-1.51 (m, 1H, LeuCH ₂β), 1.48(s, 9H, —C(CH ₃)₃), 0.98 (d, J=6.6 Hz, 6H, 2×Leu-CH ₃δ); ¹³C (CDCl₃, 125MHz): δ 172.8, 159.4, 158.3, 138.6, 135.7, 130.2, 129.8, 128.9, 128.8,128.6, 128.2, 81.3, 52.7, 44.1, 42.4, 42.1, 30.0, 28.1, 25.1, 22.9,22.2; HRMS (ES) Calculated for C₂₇H₃₇ClN₃O₃ 486.2518, found 486.2518(M+H)⁺.

tert-butyl(1-(3-azidopropyl)-2-(diphenylmethylene)hydrazine-1-carbonyl)-L-leucinate(36)

This reaction was adapted from a literature procedure.⁴⁵ Chloroalkylatedsemicarbazone 35 (2.08 g, 4.27 mmol) and sodium azide (0.833 g, 12.8mmol) were dissolved in DMF (50 mL) and heated at 60° C. for 20 h. Thereaction was cooled and had H₂O (150 mL) added to it, followed by EtOAc(3×150 mL) washes to extract organic components. Pooled EtOAc layerswere dried over Na₂SO₄, filtered, and concentrated in vacuo. The productwas purified using flash chromatography (silica gel, 10% EtOAc inhexanes), generating azide 36 as a yellow oil (1.90 g, 90%). (Rf 0.2 onSiO₂, 9:1 hexanes:EtOAc); [α]_(D) ²⁶ 53.8 (c 1.00 CHCl₃); IR (CHCl₃cast) 3411, 3061, 2958, 2871, 2097, 1734, 1683, 1499, 1446, 1368, 1257,1154 cm⁻¹; ¹H (CDCl₃, 500 MHz): δ 7.54-7.40 (m, 6H, Ar—H), 7.40-7.26 (m,4H, Ar—H), 6.74 (d, J=8.7 Hz, 1H, Leu-NH), 4.47 (ddd, J=8.8, 8.7, 5.6Hz, 1H, Leu-CHα), 3.42 (dt, J=14.7, 7.0 Hz, 1H, N—CH ₂), 3.27 (dt,J=14.7, 6.8 Hz, 1H, N—CH ₂), 3.05 (t, J=7.1 Hz, 2H, —CH ₂N₃), 1.76(ddsept, J=12.9, 7.8, 6.5 Hz, 1H, Leu-CHγ), 1.70-1.62 (m, 1H, Leu-CH₂β), 1.61-1.55 (m, 1H, Leu-CH ₂β), 1.56-1.49 (m, 2H, —CH ₂CH₂N₃), 1.48(s, 9H, —C(CH ₃)₃), 0.99 (d, J=6.6 Hz, 3H, Leu-CH₃δ), 0.98 (d, J=6.6 Hz,3H, Leu-CH ₃δ); ¹³C (CDCl₃, 125 MHz): δ 172.8, 158.5, 158.4, 138.6,135.8, 130.2, 129.8, 128.9, 128.8, 128.5, 128.3, 81.3, 52.7, 48.9, 43.4,42.1, 28.1, 26.2, 25.1, 22.9, 22.2; HRMS (ES) Calculated for C₂₇H₃₇N₆O₃493.2922, found 493.2922 (M+H)⁺.

Tert-Butyl (1-(3-azidopropyl)hydrazine-1-carbonyl)-L-leucinate (37)

This procedure was adapted from literature protocols.^(46,59,) Azide 36(1.89 g, 3.84 mmol) was dissolved in a solution of hydroxylaminehydrochloride (1.07 g, 15.4 mmol) in pyridine (75 mL) and heated to 60°C. for 22 h. The reaction was cooled to room temperature, thenconcentrated in vacuo, using CH₂Cl₂ and EtOAc co-evaporations to removeresidual pyridine. The product was purified using flash chromatography(silica gel, 60% EtOAc in hexanes, 0.1% DIPEA) yielding semicarbazide 37as a yellow oil (1.19 g, 94%). (Rf 0.5 on SiO₂, 1:1 hexanes:EtOAc);[α]_(D) ²⁶ 5.0 (c 0.92 CHCl₃); IR (CHCl₃ cast) 3406, 3335, 3216, 2958,2934, 2871, 2098, 1732, 1654, 1510, 1368, 1257, 1155 cm⁻¹; ¹H (CDCl₃,500 MHz): δ 6.67 (d, J=8.8 Hz, 1H, Leu-NH), 4.33 (ddd, J=8.9, 8.8, 5.5Hz, 1H, Leu-CHα), 3.64 (s, 2H, H ₂N—N), 3.62-3.51 (m, 2H, N—CH ₂), 3.36(t, J=6.7 Hz, 2H, —CH ₂N₃), 1.84 (app p, J=6.8 Hz, 2H, —CH ₂CH₂N₃), 1.71(ddsept, J=8.2, 8.0, 6.5 Hz, 1H, Leu-CHγ), 1.59 (ddd, J=13.6, 8.1, 5.5Hz, 1H, Leu-CH ₂β), 1.53-1.47 (m, 1H, LeuCH ₂β), 1.45 (s, 9H, —C(CH₃)₃), 0.95 (d, J=6.6 Hz, 6H, 2×Leu-CH ₃δ); ¹³C (CDCl₃, 125 MHz): δ173.5, 158.7, 81.3, 52.3, 49.2, 48.0, 42.4, 28.1, 26.3, 25.0, 22.9,22.1; HRMS (ES) Calculated for C₁₄H₂₉N₆O₃ 329.2296, found 329.2290(M+H)⁺.

(9H-fluoren-9-yl)methyl(S)-2-(2-(3-azidopropyl)-2-(((S)-1-(tert-butoxy)-4-methyl-1-oxopentan-2-yl)carbamoyl)hydrazine-1-carbonyl)pyrrolidine-1-carboxylate(38)

A solution of Fmoc-Pro-OH (1.65 g, 4.88 mmol), HATU (1.86 g, 4.88 mmol),HOAt (0.81 mL [0.6 M solution], 0.49 mmol) and DIPEA (2.13 mL, 12.2mmol) were dissolved in dry DMF (20 mL) and preactivated for 5 minutesbefore the addition of a solution of semicarbazide 37 (1.34 g, 4.07mmol) in dry CH₂Cl₂ (20 mL). The reaction mixture was stirred under Argas for 18 h then concentrated in vacuo. The crude reaction mixture wasresuspended in EtOAc (75 mL) and washed with 10% citric acid (50 mL),water (50 mL) and brine (50 mL). Pooled aqueous layers were washed withEtOAc (2×75 mL), and pooled organic fractions were dried over Na₂SO₄,filtered and concentrated in vacuo. The product was purified by flashchromatography (silica gel, 50% EtOAc in hexanes) yielding azatripeptide38 as a white solid (1.74 g, 66%). (Rf 0.4 on SiO₂, 1:1 hexanes:EtOAc);[α]_(D) ²⁶ −7.2 (c 0.83 CHCl₃); IR (CHCl₃ cast) 3357, 3229, 2957, 2872,2097, 1690, 1529, 1452, 1424, 1367, 1257, 1155 cm⁻¹; ¹H (CDCl₃, 500MHz): δ 8.20 (s, 1H, C(O)NH—N), 7.80-7.74 (m, 2H, Ar—H), 7.61-7.54 (m,2H, Ar—H), 7.47-7.37 (m, 2H, Ar—H), 7.31 (t, J=7.5 Hz, 2H, Ar—H), 6.04(d, J=8.2 Hz, 1H, Leu-NH), 4.47 (dd, J=10.5, 7.1 Hz, 1H, Fmoc-CH ₂),4.42-4.29 (m, 2H, Fmoc-CH ₂, Leu-CHα), 4.25 (t, J=6.8 Hz, 1H, Fmoc-CH),4.19 (dd, J=7.4, 4.5 Hz, 1H, Pro-CHα), 3.67-3.54 (m, 3H, 2×N—CH ₂,Pro-CH ₂δ), 3.55-3.46 (m, 1H, Pro-CH ₂δ), 3.44-3.33 (m, 2H, —CH ₂N₃),2.27 (ddd, J=11.5, 5.3, 4.9 Hz, 1H, Pro-CH ₂β), 2.17-2.06 (m, 2H, Pro-CH₂β, Pro-CH ₂γ), 2.01-1.93 (m, 1H, Pro-CH ₂γ), 1.82-1.72 (m, 2H, —CH₂CH₂N₃), 1.63 (ddd, J=13.4, 6.7, 6.5 Hz, 1H, Leu-CHγ), 1.54 (ddd, J=7.1,6.7, 6.7 Hz, 1H, Leu-CH ₂β), 1.48-1.38 (m, 10H, Leu-CH ₂β, —C(CH₃)₃),0.84 (d, J=6.5, 3H, Leu-CH ₃δ), 0.83 (d, J=6.5, 3H, Leu-CH ₃δ); ¹³C(CDCl₃, 125 MHz): δ 173.5, 170.9, 156.8, 156.0, 143.7, 141.4, 127.9,127.1, 125.0, 120.1, 81.3, 68.0, 59.2, 52.6, 49.2, 47.2, 47.1, 46.2,41.9, 28.8, 28.0, 27.2, 25.0, 24.7, 22.8, 22.1; HRMS (ES) Calculated forC₃₄H₄₆N₇O₆ 648.3504, found 648.3503 (M+H)⁺.

(2-((S)-1-(((9H-fluoren-9-yl)methoxy)carbonyl)pyrrolidine-2-carboxamido)-7-((tert-butoxycarbonyl)amino)-11,11-dimethyl-9-oxo-10-oxa-2,6,8-triazadodec-7-enoyl)-L-leucine(39)

A solution of azatripeptide 38 (0.803 g, 1.24 mmol) in dry CH₂Cl₂ (20mL) was cooled to 0° C. and had TFA (10 mL) added and stirred for 15minutes. The reaction was warmed to room temperature for 90 minutes andconcentrated in vacuo, using toluene co-evaporations to remove residualTFA. The product was resuspended in MeOH (20 mL), 10% Pd/C (25 mg) wasadded, and the reaction was stirred under an atmosphere of hydrogen gasfor 75 minutes. The reaction mixture was filtered through a pad ofCelite, concentrated in vacuo to dryness, and resuspended in dry CH₂Cl₂(20 mL) with triethylamine (0.76 mL, 5.45 mmol) and 1,3-di-Boc-2(trifluoromethylsulfonyl) guanidine (0.801 g, 2.05 mmol) for 40 h.Solvents were removed in vacuo and 39 was purified using flashchromatography (silica gel, 90% EtOAc in hexanes, 0.1% AcOH), yielding awhite solid (0.413 g, 41%). (Rf 0.05 on SiO₂, 0.1% AcOH in EtOAc);[α]_(D) ²⁶ −42.4 (c 1.00 CH3OH); IR (CH3OH cast) 3328, 2959, 1721, 1688,1642, 1530, 1419, 1335, 1156, 1136 cm⁻¹; ¹H (CDCl₃, 500 MHz): δ 9.47 (brs, 1H, Arg-NH _(ε)), 8.53 (s, 1H, C(O)NH—N), 7.75 (d, J=7.5 Hz, 2H,Ar—H), 7.56 (d, J=7.5 Hz, 1H, Ar—H), 7.54 (d, J=7.5 Hz, 1H, Ar—H), 7.39(app t, J=7.4 Hz, 2H, Ar—H), 7.30 (app t, J=7.5 Hz, 2H, Ar—H), 6.47 (brs, 1H, Leu-NH), 4.39 (dd, J=10.4, 7.1 Hz, 1H, Fmoc-CH ₂), 4.30-4.23 (m,2H, Fmoc-CH ₂, Leu-CHα), 4.23-4.17 (m, 2H, Fmoc-CH, Pro-CHα), 3.84-3.69(m, 1H, Arg-N—CH ₂β), 3.64-3.57 (m, 1H, Pro-CH ₂δ), 3.56-3.48 (m, 2H,Pro-CH ₂δ, Arg-CH ₂δN), 3.46-3.38 (m, 1H, Pro-CH ₂δ), 3.35-3.26 (m, 1H,Arg-CH ₂δN), 2.21-2.09 (m, 2H, Pro-CH ₂β, Arg-CH ₂γ), 2.09-2.01 (m, 1H,Arg-CH ₂γ), 1.93-1.86 (m, 1H, Pro-CH ₂β), 1.84-1.72 (m, 2H, Pro-CH ₂γ),1.70-1.54 (m, 3H, Leu-CH _(γ), 2×LeuCH ₂β), 1.49 (m, 9H, —C(CH ₃)₃),1.46 (s, 9H, —C(CH ₃)₃), 0.95-0.77 (m, 6H, 2×Leu-CH₃δ); ¹³C (CDCl₃, 125MHz): δ 171.8, 163.1, 158.7, 156.5, 155.3, 153.1, 143.7, 141.3, 129.0,128.2, 127.8, 127.1, 127.1, 125.3, 125.0, 120.0, 83.4, 79.8, 67.8, 58.7,53.1, 47.1, 44.9, 39.9, 37.9, 29.7, 28.3, 28.1, 27.2, 24.9, 24.5, 22.8,21.8; HRMS (ES) Calculated for C₄₁H₅₆N₇O₁₀ 806.4094, found 806.4088(M−H)⁻.

azaArg4-pyr-1-apelin-13 A2 (16)

Advanced intermediate 7 (0.2 mmol) was subjected to manual SPPS,introducing amino acids in the following order: Fmoc-Ser(tBu)-OH, 39,and Fmoc-Arg(Pmc)-OH. The resin was split into half, and Fmoc-SPPS wascontinued on 0.1 mmol scale, coupling pyr-Glu-OH. No endcapping wasperformed following addition of 39. A portion (0.05 mmol) of resin-boundpeptide was cleaved as previously described and purified using a C₁₈RP-HPLC analytical column (Method A), eluting at 13.5 min. The desiredpeptide was isolated as a white solid after lyophilization (5.5 mg, 7%).Monoisotopic MW calculated for C₆₈H₁₁₁BrN₂₃O₁₆ 528.2582, found highresolution (FTICR-ESI-MS) 528.2571 (M+3H)³⁺.

azaArg8-apelin-17 A2 (17)

The remaining 0.1 mmol carried over from the synthesis of 16 was coupledwith FmocGln(Trt)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Phe-OH,and Fmoc-Lys(Boc) OH. A portion (0.05 mmol) of resin-bound peptide wascleaved as previously described and purified using a C₁₈ RP-HPLCanalytical column (Method A), eluting at 11.1 min. The desired peptidewas isolated as a white solid after lyophilization (15.6 mg, 14%).Monoisotopic MW calculated for C₉₅H₁₆₀BrN₃₅O₂₀ 547.5435, found highresolution (FTICR-ESI-MS) 547.5430 (M+4H)⁴⁺.

Synthesis of Aza-Leucine A2 Peptides Tert-ButylO-(tert-butyl)-N-(2-(diphenylmethylene)hydrazine-1-carbonyl)-L-serinate(40)

This molecule was prepared by adapting a literature procedure.⁴⁶ Asolution of benzophenone hydrazone (1.55 g, 7.88 mmol) in dry CH₂Cl₂ (30mL) was cooled to 0° C. and cannulated into a 0° C. solution ofdisuccinimidyl carbonate (2.61 g [85% purity], 8.67 mmol) in dry CH₂Cl₂(30 mL) and dry DMF (5 mL). The reaction was warmed to room temperaturefor 45 min, then cooled down to 0° C. A 0° C. solution ofH-Ser(tBu)-OtBu.HCl (2.00 g, 7.88 mmol) and DIPEA (2.75 mL, 15.8 mmol)in dry CH₂Cl₂ (20 mL) was then cannulated into the reaction vessel andallowed to slowly come up to room temperature over 24 h. The reactionwas concentrated in vacuo and purified by flash chromatography (silicagel, 25% EtOAc in hexanes), yielding a light yellow sticky solid (2.94g, 83%). (Rf 0.4 on SiO₂, 1:1 hexanes:EtOAc); [α]_(D) ²⁶ 28.0 (c 1.0CH₂Cl₂); IR (CH₂Cl₂ cast) 3425, 3173, 3059, 2975, 2932, 1751, 1743,1693, 1518, 1367, 1161 cm⁻¹; ¹H (CDCl₃, 500 MHz): δ 7.61 (s, 1H, ═N—NH),7.58-7.45 (m, 5H, Ar—H), 7.38-7.29 (m, 3H, Ar—H), 7.29-7.23 (m, 2H,Ar—H), 7.17 (d, J=8.9 Hz, 1H, Ser-NH), 4.55 (ddd, J=8.9, 3.3, 2.9 Hz,1H, Ser-CHα), 3.88 (dd, J=8.6, 2.9 Hz, 1H, Ser-CH₂β), 3.64 (dd, J=8.6,3.3 Hz, 1H, Ser-CH₂β), 1.50 (s, 9H, C(O)OC(CH₃)₃), 1.22 (s, 9H,—CH₂OC(CH₃)₃); ¹³C (CDCl₃, 125 MHz): δ 169.9, 155.2, 147.9, 137.1,131.9, 129.7, 129.2, 128.5, 128.2, 127.1, 81.6, 73.1, 62.7, 53.8, 28.1,27.5; HRMS (ES) Calculated for C₂₅H₃₄N₃O₄ 440.2544, found 440.2549(M+H)⁺.

Tert-ButylO-(tert-butyl)-N-(2-(diphenylmethylene)-1-(2-methylallyl)hydrazine-1-carbonyl)-L-serinate(41)

Alkylation conditions were adapted from a literature procedure.⁴⁵Semicarbazone 40 (0.945 g, 2.15 mmol) was dissolved in THF (10 mL) andcooled to 0° C. Aqueous tetraethylammonium hydroxide (7.91 mL [20%solution], 10.8 mmol) was added and stirred for 30 minutes, followed bythe addition of 3-bromo-2-methylpropene (1.63 mL, 16.1 mmol) at 0° C.The reaction was slowly warmed to room temperature and was quenchedafter 60 h by the addition of 10% citric acid (15 mL) followed by brine(15 mL). Organic components were extracted with EtOAc (3×75 mL), driedover Na₂SO₄, filtered and concentrated in vacuo. Alkylated semicarbazone41 was purified by flash chromatography (silica gel, 20% EtOAc inhexanes) and was isolated as a yellow oil (1.06 g, 99%). (Rf 0.6 onSiO₂, 3:1 hexanes:EtOAc); [α]_(D) ²⁶ 6.1 (c 0.75 CH2Cl2); IR (CH₂Cl₂cast) 3421, 3062, 2974, 2935, 2877, 1745, 1687, 1496, 1366, 1154, 1098cm⁻¹; ¹H (CDCl₃, 500 MHz): δ 7.50-7.39 (m, 6H, Ar—H, Ser-NH), 7.39-7.34(m, 1H, Ar—H), 7.32-7.27 (m, 4H, Ar—H), 4.71 (dq, J=1.4, 1.1 Hz, 1H,=CHH), 4.58 (ddd, J=8.9, 3.2, 3.2 Hz, 1H, Ser-CHα), 4.48-4.43 (m, 1H,═CHH), 3.98 (d, J=17.0 Hz, 1H, Leu-NCH ₂β), 3.88-3.79 (m, 2H, Ser-CH ₂β,Leu-NCH ₂β), 3.62 (dd, J=8.6, 3.3 Hz, 1H, Ser-CH ₂β), 1.48 (s, 9H,C(O)OC(CH ₃)₃), 1.41-1.32 (m, 3H, —CH ₃), 1.17 (s, 9H, —CH₂OC(CH ₃)₃);¹³C (CDCl₃, 125 MHz): δ 170.2, 158.5, 154.1, 139.8, 139.2, 135.9, 129.5,129.4, 128.3, 128.2, 128.0, 111.8, 81.3, 72.9, 62.8, 54.7, 50.6, 28.1,27.4 19.5; HRMS (ES) Calculated for C₂₉H₄₀N₃O₄ 494.3013, found 494.3010(M+H)⁺.

Tert-Butyl O-(tert-butyl)-N-(1-isobutylhydrazine-1-carbonyl)-L-serinate(42)

Alkylated semicarbazone 41 (2.19 g, 4.43 mmol) was dissolved in MeOH (50mL) and had 10% Pd/C (20 mg) added. The suspension was stirred underhydrogen gas for 20 h, filtered through a pad of Celite, andconcentrated in vacuo. The crude residue purified using flashchromatography (silica gel, 50% EtOAc in hexanes), yieldingsemicarbazide 42 as a yellow oil (1.37 g, 93%). (R_(f) 0.6 on SiO₂, 3:1hexanes:EtOAc); [α]_(D) ²⁶ 20.8 (c 0.45 CH₂Cl₂); IR (CH₂Cl₂ cast) 3420,3331, 3217, 2974, 2934, 2873, 1741, 1656, 1509, 1366, 1232, 1157, 1100cm⁻¹; ¹H (CDCl₃, 500 MHz): δ 7.04 (d, J=9.0 Hz, 1H, Ser-NH), 4.45 (ddd,J=9.0, 3.1, 3.0 Hz, 1H, Ser-CHα), 3.78 (dd, J=8.6, 3.1 Hz, 1H, Ser-CH₂β), 3.56 (s, 2H, H₂N—N), 3.52 (dd, J=8.6, 3.2 Hz, 1H, Ser-CH ₂β), 3.36(dd, J=13.9, 7.7 Hz, 1H, Leu-NCH ₂β), 3.26 (dd, J=13.9, 7.4 Hz, 1H,Leu-NCH ₂β), 2.01-1.89 (m, 1H, Leu-CHγ), 1.46 (s, 9H, C(O)OC(CH ₃)₃),1.14 (s, 9H, —CH₂OC(CH ₃)₃), 0.92 (d, J=6.7 Hz, 3H, Leu-CH ₃δ), 0.91 (d,J=6.7 Hz, 3H, Leu-CH ₃δ); ¹³C (CDCl₃, 125 MHz): δ 170.8, 159.1, 81.1,72.8, 63.1, 57.4, 54.4, 28.1, 27.4, 26.1, 19.9; HRMS (ES) Calculated forC₁₆H₃₄N₃O₄ 332.2544, found 332.2539 (M+H)⁺.

Tert-ButylN-(2-((S,)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-5-((((2-chloro-benzyl)oxy)carbonyl)amino)pentanoyl)-1-isobutylhydrazine-1-carbonyl)-O-(tert-butyl)-L-serinate(43)

A solution of Fmoc-Orn(2-Cl-Cbz)-OH (2.59 g, 4.91 mmol), HATU (1.87 g,4.91 mmol), HOAt (0.82 mL [0.6 M solution], 0.49 mmol) and DIPEA (2.14mL, 12.3 mmol) were dissolved in dry DMF (20 mL) and preactivated for 5minutes before the addition of a solution of semicarbazide 42 (1.36 g,4.09 mmol) in dry CH₂Cl₂ (20 mL). This reaction was stirred under Ar for30 h then concentrated in vacuo. The crude reaction was resuspended inEtOAc (100 mL) and washed with 10% citric acid (2×100 mL) and brine (100mL). Pooled aqueous layers were washed with EtOAc (2×100 mL), and pooledorganic fractions were dried over Na₂SO₄, filtered and concentrated invacuo. The reaction was purified by flash chromatography (silica gel,40% EtOAc in hexanes) yielding azatripeptide 43 as a white solid (2.64g, 77%), with a 17% recovery of 42. (R_(f)0.2 on SiO₂, 1:1hexanes:EtOAc); [α]_(D) ²⁶ 11.8 (c 1.00 CHCl₃); IR (CHCl₃ cast) 3321,3007, 2974, 2934, 2873, 1700, 1657, 1523, 1450, 1367, 1247, 1157 cm⁻¹;¹H (CDCl₃, 500 MHz): δ 8.31 (s, 1H, C(O)NH—N), 7.79-7.74 (m, 2H,Fmoc-Ar—H), 7.59 (d, J=7.5 Hz, 2H, Fmoc-Ar—H), 7.39 (m, 4H, 2×Fmoc-Ar—H,2×2-Cl—Ar—H), 7.34-7.28 (m, 2H, Fmoc-Ar—H), 7.27-7.23 (m, 2H,2×2-Cl—Ar—H), 5.82 (d, J=8.2 Hz, 1H, Ser-NH), 5.53 (d, J=7.8 Hz, 1H,Orn-NHα), 5.27-5.20 (m, 2H, —OCH ₂ (2-Cl)Ph, Orn-NH _(ε)), 5.16 (d,J=13.0 Hz, 1H, —OCH ₂(2-Cl)Ph), 4.48-4.38 (m, 3H, Ser-CHα, Orn-CHα,Fmoc-CH ₂), 4.38-4.32 (m, 1H, Fmoc-CH ₂), 4.21 (t, J=7.0 Hz, 1H,Fmoc-CH), 3.71 (dd, J=8.8, 2.8 Hz, 1H, Ser-CH ₂β), 3.54-3.45 (m, 2H,Ser-CH ₂β, Orn-CH ₂δ), 3.44-3.36 (m, 1H, Leu-NCH ₂β), 3.33-3.24 (m, 1H,Leu-NCH ₂β), 3.24-3.15 (m, 1H, Orn-CH ₂δ), 2.00-1.90 (m, 1H, Orn-CH ₂δ),1.86-1.77 (m, 1H, Leu-CHγ), 1.75-1.56 (m, 3H, Om-CH ₂β, 2×Orn-CH ₂γ),1.41 (s, 9H, C(O)OC(CH ₃)₃), 1.08 (s, 9H, —CH₂OC(CH ₃)₃, 0.89 (d, J=6.6Hz, 6H, 2×Leu-CH ₃O); ¹³C (CDCl₃, 125 MHz): δ 173.7, 170.2, 157.1,156.7, 156.4, 143.6, 141.3, 134.1, 133.5, 129.7, 129.5, 129.4, 127.8,127.1, 126.8, 125.1, 120.0, 81.6, 72.9, 67.3, 64.1, 62.6, 55.4, 54.5,52.1, 47.1, 39.7, 29.8, 28.0, 27.3, 26.9, 26.2, 20.0, 20.0; HRMS (ES)Calculated for C₄₄H₅₉ClN₅O₉ 836.3996, found 836.4008 (M+H)⁺.

N-(2-((S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-5-((((2-chlorobenzyl)oxy)carbonyl)amino)pentanoyl)-1-isobutylhydrazine-1-carbonyl)-O-(tert-butyl)-L-serine(44)

Azatripeptide 43 (1.21 g, 1.44 mmol) was dissolved in toluene (100 mL)and had flash-grade silica (25.0 g) added. This suspension was refluxedat 115° C. for 95 minutes, checking TLC and LC-MS every 30 minutes. Thereaction was cooled to room temperature and a 10% MeOH in CH₂Cl₂solution (100 mL) was added, then filtered through a pad of Celite. Thereaction was concentrated in vacuo, and purified by flash chromatography(silica gel, 0-2% MeOH in EtOAc, 0.1% AcOH). The desired product wasobtained as a sticky white solid (0.770 g, 69%). (R_(f) 0.3 on SiO₂, 1:4hexanes:EtOAc, 0.1% AcOH); [α]_(D) ²⁶ 14.5 (c 1.00 CHCl₃); IR (CHC1₃cast) 3313, 3018, 2971, 2874, 1697, 1528, 1450, 1249, 1193, 1104 cm⁻¹;¹H (CDCl₃, 500 MHz): δ 8.10 (s, 1H, C(O)NH—N), 7.71 (d, J=7.6 Hz, 2H,Fmoc-Ar—H), 7.54 (d, J=7.5 Hz, 2H, Fmoc-Ar—H), 7.40-7.29 (m, 4H,2×Fmoc-Ar—H, 2×2-Cl—Ar—H), 7.29-7.16 (m, 4H, 2×Fmoc-Ar—H, 2×2-Cl—Ar—H),6.05 (br s, 1H, Ser-NH), 5.53 (br s, 1H, Orn-NHα), 5.22-5.11 (m, 2H,—OCH ₂(2-Cl)Ph), 4.42-4.37 (m, 2H, Ser-CHα, Fmoc-CH ₂), 4.35-4.27 (m,1H, Orn-CHα), 4.21 (dd, J=10.1, 8.7 Hz, 1H, Fmoc-CH ₂), 4.14 (t, J=8.3Hz, 1H, Fmoc-CH), 3.76-3.68 (m, 1H, Ser-CH ₂β), 3.52-3.46 (m, 1H, Ser-CH₂β), 3.33-3.13 (m, 4H, 2×Orn-CH ₂δ, 2×Leu-NCH ₂β), 1.89-1.80 (m, 1H,Orn-CH ₂β), 1.79-1.65 (m, 2H, Om-CH ₂β, Leu-CHγ), 1.62-1.54 (m, 2H,Orn-CH ₂γ), 1.02 (s, 9H, —CH₂OC(CH ₃)₃), 0.83 (d, J=6.5 Hz, 3H, Leu-CH₃δ), 0.81 (d, J=6.5 Hz, 3H, Leu-CH ₃δ); ¹³C (CDCl₃, 125 MHz): δ 171.8,170.4, 159.7, 158.3, 156.6, 143.6, 141.2, 134.2, 133.4, 129.6, 129.5,129.3, 127.8, 127.1, 126.9, 125.1, 120.0, 73.6, 67.3, 63.9, 62.1, 55.7,55.2, 52.5, 47.0, 39.9, 29.7, 27.3, 27.0, 25.9, 20.0; HRMS (ES)Calculated for C₄₀H₄₉ClN₅O₉ 778.3224, found 778.3208 (M−H)⁻.

N—((S)-5-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-10-((tert-butoxycarbonyl)amino)-2-isobutyl-14,14-dimethyl-4,12-dioxo-13-oxa-2,3,9,11-tetraazapentadec-10-enoyl)-0-(tert-butyl)-L-serine(45)

A solution of 44 (0.730 g, 0.94 mmol) in MeOH (50 mL) had 10% Pd/C (25mg) added, and the suspension was stirred under an atmosphere ofhydrogen gas for 135 minutes. The reaction mixture was filtered througha pad of Celite, concentrated in vacuo to dryness, and resuspended indry CH₂C₀₁₂ (30 mL) with triethylamine (0.59 mL, 4.21 mmol) and1,3-di-Boc-2-(trifluoromethylsulfonyl)guanidine (0.549 g, 1.40 mmol) for30 h. Solvents were removed in vacuo and the azatripeptide product waspurified using flash chromatography (silica gel, 90% EtOAc in hexanes,0.1% AcOH), yielding white solid 45 (0.161 g, 20%). (R_(f) 0.1 on SiO₂,1:4 hexanes:EtOAc, 0.1% AcOH); [α]_(D) ²⁶ 2.3 (c 0.85 CHCl₃); IR (CHCl₃cast) 3326, 2978, 2934, 1722, 1644, 1531, 1368, 1331, 1136, 1054 cm⁻¹;¹H (CDCl₃, 500 MHz): δ 8.94 (br s, 1H, C(O)NH—N), 8.46 (br s, 1H, Arg-NH_(ε)), 7.75 (d, J=7.6 Hz, 2H, Ar—H), 7.58 (d, J=7.6 Hz, 2H, Ar—H), 7.39(t, J=7.5 Hz, 2H, Ar—H), 7.30 (t, J=7.5 Hz, 2H, Ar—H), 6.16 (br s, 1H,Arg-NHα), 6.08 (s, 1H, Ser-NH), 4.49-4.40 (m, 3H, Arg-CHα, Ser-CHα,Fmoc-CH ₂), 4.34-4.28 (m, 1H, Fmoc-CH ₂), 4.18 (t, J=7.0 Hz, 1H,Fmoc-CH), 3.81-3.75 (m, 1H, Ser-CH ₂β), 3.61-3.49 (m, 1H, Ser-CH ₂β),3.49-3.24 (m, 4H, 2×Arg-CH ₂δ, 2×Leu-NCH ₂β), 1.92-1.83 (m, 1H, Arg-CH₂β), 1.81-1.60 (m, 4H, Arg-CH ₂β, 2×Arg-CH ₂γ, Leu-CHγ), 1.50 (s, 9H,Arg-C(CH ₃)₃), 1.47 (s, 9H, Arg-C(CH ₃)₃), 1.12 (s, 9H, —CH₂OC(CH ₃)₃),0.91-0.85 (m, 6H, 2×Leu-CH ₃δ); ¹³C (CDCl₃, 125 MHz): δ 171.1, 170.2,163.3, 162.4, 157.7, 156.5, 153.2, 143.7, 141.3, 127.8, 127.1, 125.0,120.0, 83.6, 79.9, 74.7, 67.3, 61.5, 55.8, 54.0, 53.1, 47.1, 40.4, 29.4,28.3, 28.0, 27.3, 27.0, 25.5, 20.2, 20.1; HRMS (ES) Calculated forC₄₃H₆₄N₇O₁₁ 854.4658, found 854.4654 (M+H)⁺. azaLeu5-pyr-1-apelin-13 A2(18)

Advanced intermediate 7 (0.2 mmol) was subjected to manual SPPS,introducing amino acids in the following order: 45, Fmoc-Pro-OH, andFmoc-Arg(Pmc)-OH. The resin was split into half, and Fmoc-SPPS wascontinued on 0.1 mmol scale, coupling pyr-Glu-OH. No endcapping wasperformed following addition of 45. A portion (0.05 mmol) of resin-boundpeptide was cleaved as previously described and purified using a C₁₈RP-HPLC analytical column (Method A), eluting at 13.3 min. The desiredpeptide was isolated as a white solid after lyophilization (4.8 mg, 6%).Monoisotopic MW calculated for C₆₈H₁₁₁BrN₂₃O₁₆ 528.2582, found highresolution (FTICR-ESI-MS) 528.2576 (M+3H)³⁺.

azaLeu9-pyr-1-apelin-13 A2 (19)

The remaining 0.1 mmol carried over from the synthesis of 18 was coupledwith Fmoc-Gln(Trt)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Arg(Pmc)-OH, Fmoc-Phe-OH,and Fmoc-Lys(Boc)-OH. A portion (0.05 mmol) of resin-bound peptide wascleaved as previously described and purified using a C₁₈ RP-HPLCanalytical column (Method A), eluting at 11.3 min. The desired peptidewas isolated as a white solid after lyophilization (4.4 mg, 4%).Monoisotopic MW calculated for C₉₅H₁₆₀BrN₃₅O₂₀ 547.5435, found highresolution (FTICR-ESI-MS) 547.5420 (M+4H)⁴⁺.

Example 8 In Vitro NEP Stability

This experiment compared the in vitro NEP stability of the Arg/Leupeptides of the embodiments to native apelin isoforms and their A2substituted counterparts. Peptides were incubated with recombinant humanNEP (rhNEP, Sino Biological) at 37° C. for up to 72 h, and the extent ofdegradation was analyzed via LC-MS because of the overlapping elutionpatterns of peptide fragments. FIG. 9 demostrates in vitro NEPdegradation trends for a) pyr-1-apelin-13 peptides and b) apelin-17peptides, comparing native apelin isoforms (1, 2), ACE2-resistantpeptides (4, 5) and novel Arg/Leu substituted peptides 8-19. Nativeapelin isoforms (1, 2) and their respective A2 substituted peptides (4,5) were degraded by NEP at rates comparable to those previouslyreported. (McKinnie, S. M. K., et al. ChemBioChem: 17, 1495-1498(2016)). Peptide 5 interestingly showed increased susceptibility to NEPdespite all synthetic modifications being at minimum 6 amino acids (P6′)away from the site of endoprotease cleavage. Distal amino acidsubstitutions have been shown to modulate NEP proteolysis in thebreakdown of Ap and synthetic substrates (Almenoff, J. et al.,Biochemistry: 22, 590-599 (1983)) and previous in vitro plasmadegradation experiments observed that C-terminal modifications to apelinpeptides markedly affected the presence of key peptide fragments (Murza,A. et al., Biopolymers: 101, 297-303 (2014)). When examining the impactof Arg/Leu-substitution, all peptides 8-19 showed dramatically improvedproteolytic stability to NEP compared to either native peptide (1, 2) orthe corresponding A2 substituted peptides (4, 5). Overall,Arg/Leu-substituted apelin-17 A2 peptides showed an enhanced stabilitycompared to the pyr-1-apelin-13 A2 peptides. However, the proteolysis ofthese peptides was not due to degradation at either location associatedwith NEP endoprotease activity. Instead, peptides were slowly degradedbetween Nle-Aib within the A2-modified C-terminus. NEP does havesignificant carboxydipeptidase activity as exemplified in thedegradation of neurological enkephalin pentapeptides (Nalivaeva, N. N.et al., Handbook of Proteolytic Enzymes: 3rd Edn, Elsevier Ltd., 612-619(2013)) and key amino acids have been implicated in binding andorienting the C-terminus of the peptide substrate to facilitateproteolysis. (Dion, N., et al., Biochem. J.: 311, 623-627 (1995);Bateman Jr., R. C., et al., J. Biol. Chem.: 264, 6151-6157 (1989);McMurray, J. J. et al., J. Med.: 371, 993-1004 (2014)). C-terminaldipeptide excision was not observed with native isoforms 1-3, likely dueto the unfavorable geometry of proline in the P1′ position. Pro to Aibsubstitution in the A2 peptide series was observed to enable anadditional NEP in vitro proteolytic site.

This experiment investigates the ability of synthetic peptides 8-19 toinhibit the inherent proteolytic activity of NEP. Followingpreincubation of NEP with equimolar concentrations of 8-19, degradationof 1 was nearly identical in either the presence or absence of peptides,suggesting that in vitro proteolytic activity is not significantlyimpacted.

Example 9

In Vitro Peptide Stability—Plasma

This experiment explored the in vitro plasma stability of syntheticapelin peptides 8-19. Triplicate assessments were performed in humanblood plasma and analyzed by RP-HPLC (Table 3). (Wang, W., et al.,Hypertension: 68, 365-37 (2016)).

TABLE 3 pyr-1-apelin-13 peptides apelin-17 peptides Arg-Leu % apelin %apelin % apelin % apelin modification peptide 30 min 60 min peptide 30min 60 min none (native) 1 45 ± 8  12 ± 2 2 51 ± 17 39 ± 7 none (A2) 477 ± 19  65 ± 14 5 43 ± 1  35 ± 5 D-Leu 8 32 ± 2  22 ± 1 9 80 ± 3  80 ±4 NMeLeu 10 77 ± 3  59 ± 6 11 49 ± 10 47 ± 7 αMeArg 12 +i 62 ± 6 13 61 ±10 55 ± 4 αMeLeu 14 45 ± 6  38 ± 3 15 77 ± 4  48 ± 7 azaArg 16 83 ± 3 57 ± 1 17 96 ± 6  94 ± 3 azaLeu 18 19 ± 5   2 ± 1 19 82 ± 1  68 ± 4

Arg/Leu substitution had a varying impact on the different apelinisoforms. With the exception of 11, apelin-17 A2 peptides showedenhanced stability compared to native 2 or A2-substitued peptide 5. Mostnotably, azaArg8 peptide 17 showed very little degradation during thetime course examined. In contrast, there was a much greater range of invitro stabilities when examining the Arg/Leu substituted pyr-1-apelin-13A2 peptides. Peptides substituted at the Arg4 position (12, 16) ordirectly on the susceptible amide bond (10) showed comparable stabilityto that of 4, while Leu5-modified peptides (8, 14, 18) showed enhancedproteolysis compared to native 1 or A2-modified peptide 4. Based on theprevious kinetic studies (McKinnie, S. M. K., et al., ChemBioChem: 17,1495-1498 (2016)) and combined in vitro NEP and plasma pharmacokinetics,NEP proteolysis appears to be more significant in the degradation ofapelin-17 isoforms. However, the enhanced in vitro stabilities ofArg/Leu-modified peptides to both NEP and nonspecific plasma proteolysiswere encouraging prior to interrogating their individual physiologicalactivities.

Example 10 Binding Affinity of Apelin Peptides

This experiment evaluated the ability of peptides of the presentembodiments to bind to the wild-type rat apelin receptor, in order toexamine the impact of synthetic modification within the critical RPRLmotif of the apelin peptides. Membrane preparations from CHO cellsstably expressing the wild-type rat apelin receptor tagged at itsC-terminus with EGFP were generated as previously described (Gerbier, R,et al., FASEB J., 29, 314-322 (2015)) and the affinities of nativeisoforms 1 and 2, parent peptides 4 and 5, and Arg/Leu-peptides 8-19were determined by their abilities to displace [¹²⁵I]-pyr-1-apelin-13(0.2 nM). Native isoforms 1 and 2 inhibited specific binding to thewild-type rat apelin receptor with inhibitory constant (Ki) values of0.3 and 0.05 nM respectively (Table 3).

TABLE 3 pyr-1-apelin-13 peptides apelin-17 peptides Ara-Leu Affinity* KiAffinity Ki modification peptide (nM) peptide (nM) none (native)  1  0.3± 0.07 (4)  2 0.053 ± 0.009 (4) none (A2)  4   2 ± 0.3 (3)  5  0.19 ±0.025 (3) D-Leu  8 0.12 ± 0.035 (3)  9  0.14 ± 0.056 (3) NMeLeu 10 0.10± 0.048 (3) 11  0.45 ± 0.110 (3) α MeArg 12 0.56 ± 0.033 (3) 13  0.13 ±0.032 (3) α MeLeu 14 0.17 ± 0.050 (3) 15  0.18 ± 0.079 (3) azaArg 16   1± 0.10 (3) 17  0.14 ± 0.009 (3) azaLeu 18 0.13 ± 0.063 (3) 19  0.15 ±0.015 (3) *Affinity values are means ± SE (n), with n representing thenumber of independent experiments performed in duplicate.

Pyr-1-apelin-13 peptides 8, 10, 14, and 18 showed a modest improvementin receptor binding, while parent peptide pyr-1-apelin-13 A2 (4),azaArg4-pyr-1-apelin-13 A2 (16), and αMeArg4-pyr-1-apelin-13 A2 (12)exhibited a slightly weaker affinity compared to 1 (by a factor 6, 3,and 2 respectively). In contrast, Arg/Leu substitution slightly reducedthe binding affinity of all apelin-17 peptides compared to native 2,exhibiting Ki values in the subnanomolar range, about three times lesspotent. However, these data showed no drastic effect on in vitro apelinreceptor binding, thus supporting the hypothesis that the selectedsynthetic modifications within the RPRL motif of apelin were notdeleterious for receptor binding.

Example 11 Binding Physiological Experiments

Synthetic peptides 8-19 were tested for blood pressure loweringabilities in anesthetized mice. Apelin peptides were injected throughthe carotid artery, monitoring blood pressure (BP) and heart rate (HR)over 60 minutes. Surprisingly, the potent physiological effects of 4were not observed with any of the Arg/Leu-substituted pyr-1-apelin-13 A2peptides (FIG. 10A). Conservative substitutions such as epimerization(8) or N-methylation (10) at the Leu5 position showed no ability todecrease blood pressure in this assay. However, peptides (10, 14, 16)did have a significant and pronounced effect of increasing the murine HRfollowing injection. Tachycardia is directly correlated with nativeapelin isoforms binding to the receptor (Cheng, X., et al., EuropeanJournal of Pharmacology: 470, 171-175, 2003) and suggests that thesepeptides, while not fully functional, still have some inherentphysiological activities.

This differential physiological activity was further observed wheninvestigating the impact of the same substitutions on the apelin-17 A2isoform. All Arg/Leu modifications, even those inactive in the 13 A2isoform, showed an ability to induce tachycardia. Most significantly,three peptides (11, 17, 19) showed potent hypotensive activity thatrivaled or bested that of native 2 or A2 variant 5 (FIG. 10B). Peptidesthat retained activity involved N-methyl Leu9 peptide 11 and bothconformationally flexible aza-peptides 17 and 19, suggesting that thesesynthetic modifications in the apelin-17 framework were flexible orconservative enough to induce full biological activity upon binding tothe apelin receptor.

Example 12 Ischemic Heart Disease

Peptides that showed hypotensive activity were further examined fortheir abilities to prevent myocardial ischemic reperfusion injury usingthe Langendorff protocol. Stable isolated rat hearts were exposed to a30-minute period of ischemia, then reperfused with: saline (vehicle);native 2; vasoactive peptides 11, 17, 19; or inactive 18; in apost-conditioning protocol. The ex vivo heart was assessed for a varietyof parameters (heart rate (HR); left ventricle developed pressure(LVDP); maximum derivative of change in systolic pressure over time (maxdP/dt); minimum derivative of change in diastolic pressure over time(min dP/dt); and rate-pressure product (RPP)) indicative of generalheart function and performance (FIG. 11).

Following Langendorff experiments, the potent hypotensive apelin-17 A2peptides 11, 17, and 19 showed an equivalent ability to rescue the heartfrom ischemic reperfusion injury compared to native isoform 2. In allassessed parameters, these peptides showed full potency, with 17behaving very analogously to 2, while 11 and 19 showed a slightimprovement over the native isoform in max/min dP/dt, LVDP and RPP. Itwas observed that the inactive pyr-1-apelin-13 A2 peptide 18 behavedcomparably to that of the negative saline control.

Synthetic substitution of the site of NEP proteolysis gave rise to threepotent peptides (11, 17, and 19) with full beneficial cardiovascularactivities, sub-nanomolar receptor affinities, and improved in vitro NEPand plasma stabilities. As well, these peptides showed no ability toinhibit the inherent activity of NEP. Further optimization of the twoapelin-17 A2 azapeptide derivatives (17, 19) due to their improvedpharmacokinetics is encouraging in the pursuit of an apelin peptide withpractical therapeutic applicability. This study additionally providesinsight into the limited tolerance to modification within the ‘RPRL’motif, and further supports its significant role in the apelinergicsystem. Most notably, any Arg/Leu modification abolished full agonisticactivity within the pyr-1-apelin-13 A2 scaffold. Even conservativesubstitutions employed such as epimerization, N- or a-methylations, ora-carbon replacement with nitrogen failed to retain full physiologicalactivity despite having comparable in vitro apelin receptor binding. Thefact that some of the Arg/Leu modifications show potency in theapelin-17 A2 series suggests that the longer N-terminal extension iscapable of facilitating the appropriate receptor interactions andinternalization necessary to induce full physiological activity.

The inactivity of both D-Leu substituted peptides 8 and 9 wasparticularly surprising because of literature precedent that D-Leupyr-1-apelin-13 retained acceptable abilities to bind (˜10-fold decreasein affinity) and inhibit forskolin-induced cAMP accumulation.29Epimerization within or adjacent to an inducible structural element suchas a β-turn would likely be detrimental to activity. However, a recentapelin-17 peptide (P92) with full agonistic activity has been reportedwith multiple epimerizations, including two flanking both the N-(D-Gln)and C-(D-Leu) termini of the “RPRL” region. Gerbier, et. al.,“Development of original metabolically-stable apelin-17 analogs withdiuretic and cardiovascular effects,” FASEB J., 2017, 31, 687-700. Thispeptide has additional substitutions that make direct comparison withour peptides difficult, but it is encouraging to know that physiologicalactivity and stability can be enhanced through epimerizations.

Select pyr-1-apelin-13 A2 (10, 14, 16) and apelin-17 A2 (9, 13, 15)peptides had an impact on the heart rate of mice following perfusionwithout inducing any vasoactive effects. This may be rationalizedthrough the biased agonism of these peptides for G-protein pathwaysinstead of being internalized. It is known that p-arrestin recruitmentand internalization initiates vasodilation and additionalcardioprotective effects of apelin, and the C-terminal phenylalanine ofapelin plays a critical role in this process.

Example 13 In Vitro Protease Experiments Neprilysin Degradation Assays

Apelin peptides were dissolved in Milli-Q water (1 mM). Recombinanthuman neprilysin (rhNEP, Sino Biological) was reconstituted in Trisbuffer (100 mM Tris, 100 mM NaCl, 10 μM ZnCl₂, pH 7.5). To initiate theassay, rhNEP was diluted in Tris buffer (3.1 nM final concentration),and preincubated at 37° C. for 10 minutes prior to the addition of 5 μLof apelin peptide (1 mM) and 1.5 μL internal standarddansyl-Tyr-Val-Gly-OH (1 mM). Aliquots (10 μL) were removed at 0, 1, 4,24, and 72 h, quenched with 0.1 M EDTA (10 μL), diluted to 100 μL withMilli-Q water and analyzed by LC-MS. Assays were performed in triplicate(n=3) for each time point. Integrated peak areas of the parent apelinpeptide and internal standard derived from LC-MS analyses, wereextracted using Mass Hunter software (version B.04.00) and compared inpositive extracted ion count modus (+EIC, extracted-ion chromatogram).The extent of proteolysis was compared in positive extracted ion countmodus (+EIC). The extent of proteolysis was apelin peptide to theinternal dansyl-YVG standard (apelin:dansyl-YVG), to the same ratio atthe different assay time points. The decrease in apelin:dansyl-YVG ratiowas converted to a percentage of cleaved peptide over time.

Neprilysin Inhibition Assays

A solution of rhNEP (3.1 nM in 100 mM Tris, 100 mM 1118 NaCl, 10 μMZnCl₂, pH 7.5) was preincubated with 5 μL of apelin peptide (1 mM) and1.5 μL internal standard dansyl-Tyr-ValGly-OH (1 mM, dansyl-YVG-OH,Sigma-Aldrich) at 37° C. for 10 min prior to the addition of 5 μLpyr-1-apelin-13 (1 mM). Aliquots (10 μL) were removed at 0, 1, 4, 24,and 72 h, and quenched and analyzed as previously described. Assays wereperformed in duplicate (n=2) for each time point.

Isolation and Quantification of Apelin Peptides from Plasma

20 μL of plasma was portioned into microfuge tubes and pre-warmed to 37°C. 5 μL of apelin peptide (400 μM) was added and incubated at 37° C. forvarying lengths of time. Experiments were quenched by the addition of 20μL of 10% aqueous TFA. 5 μL of internal standard (1 mMdansyl-Tyr-Val-Gly-OH) was added and experiments were diluted up to 100μL with 0.1% aqueous TFA. These assays were loaded onto apre-equilibrated C₁₈ spin column (Harvard Apparatus), which hadpreviously been wet with 2×300 μL 50% acetonitrile in 0.1% aqueous TFAand 2×300 μL 0.1% aqueous TFA respectively, centrifuging at 300×g for 2minutes between each 300 μL aliquot. Quenched plasma assays werecentrifuged at 300×g until the sample was loaded. The resultant filtratewas reloaded onto the column along with 100 μL 0.1% aqueous TFA andcentrifuged at 300×g two additional times. The desired plasma peptideswere washed by the addition of 2×300 μL 0.1% aqueous TFA and centrifugedat 300×g for 2 min, discarding the filtrate after each wash. Desiredpeptides were eluted by the addition of 300 μL of 40% acetonitrile(human plasma) in 0.1% aqueous TFA and centrifugation at 300×g for 2minutes. Eluted samples were diluted with 0.1% aqueous trifluoroaceticacid prior to analysis by C18 RP-HPLC. To analyze the remainingpercentage of apelin peptides in plasma, incubations. of pyr-1-apelin-13or apelin-17 in plasma were immediately quenched, worked up and analyzedby C18RP-HPLC as previously described, and the ratio of apelin peptideto internal standard was calculated based on the area under the peaks.This 0 minute incubation ratio was used to compare the apelinpeptide:internal standard ratios for the time experiments.

Radioligand Binding Experiments

Membrane preparations from CHO cells stably expressing the wild-type ratapelin receptor-EGFP were prepared as previously described (Gerbier etal., New Structural Insights Into The Apelin Receptor: Identification OfKey Residues For Apelin binding; FASEB J. 2015, 29, 314-322; Iturriozet. al., Development Of Original Metabolically-Stable Apelin-17 PeptidesWith Diuretic And Cardiovascular Effects; FASEB J. 2017, 31, 687-700.)Crude membrane preparations (1 μg total mass of membranes/assay) wereincubated for 3 h at 20° C. with 0.2 nM [¹²⁵I]-pyr-1-apelin-13(monoiodinated on Lys⁸ with Bolton-Hunter reagent, Perkin Elmer,Wellesley, Mass., USA) in binding buffer (50 mM HEPES, 5 mM MgCl2 1149pH 7.5, BSA 1%) alone or in presence of the different compounds atvarious concentrations. The reaction was stopped by adding 4 mL of coldbinding buffer, filtered on Whatman GF/C filters and washed with 5 mL ofcold binding buffer. Radioactivity was then counted using a Wizard 1470Wallac gamma counter (Perkin Elmer, Turku, Finland). Binding experimentdata were analyzed with GraphPad Prism.

Blood Pressure Assays

Mice were anaesthetized with 1.5% isoflurane/oxygen, and bodytemperature was monitored and maintained at 36° C. by a heating pad. Theaorta was cannulated via the right carotid artery using a PV loopcatheter (Model 1.2F from Scisense, Transonic) in order to continuouslyrecord arterial blood pressure and heart rate (LabScribe 2.0, Scisense).Peptides 1, 2, 4, 5, 8-19 (1.4 μM/kg body weight) or the same volume ofsaline were injected via the right jugular vein. Results are reported assystolic blood pressure (SBP), diastolic blood pressure (DBP), meanarterial blood pressure (MABP) and heart rate (HR).

Langendorff Isolated Heart Technique

Langendorff heart perfusion and ischemia-reperfusion injury wereprepared and cardiac function was measured. Mice were heparinized andanaesthetized with 1.5-2% isoflurane inhalation. The heart was excised,mounted on a Langendorff system, and perfused at a consistent pressureof 80 mmHg with modified Krebs-Henseleit solution (116 mM NaCl, 3.2 mMKCl, 2.0 mM CaCl₂, 1.2 mM MgSO₄, 25 mM NaHCO₃, 1.2 mM KH₂PO₄, 11 mMglucose, 0.5 mM EDTA and 2 mM pyruvate), which was kept at 37° C. andcontinuously oxygenated with 95% 02 and 5% CO₂ which maintained theperfusion buffer at pH 7.4. After stabilization and 10 min baselinerecording, global ischemia was induced for 30 min followed by 40 min ofreperfusion. Apelin 17 (2) or apelin peptides (11, 17, 18, or 19) weregiven at the start of reperfusion for 10 min at a concentration of 1 μM.Left ventricular functions were obtained continuously by PowerLab system(ADInstruments, Australia). Data was reported as mean value of every 5min. Left ventricular functions were reported as: Left VentricularDeveloped Pressure (LVDP); Heart rate (HR); maximum derivative of changein systolic pressure over time (max dP/dt); minimum derivative of changein diastolic pressure over time (min dP/dt); and Rate Pressure Product(RPP).

Example 14 Elucidation of KLKB1

Isolation and Quantification of Apelin-17A2 (5) from Plasma.

20 μL of plasma was portioned into microfuge tubes and prewarmed to 37°C. 5 μL of apelin peptide (400 μM) was added and incubated at 37° C. forvarying lengths of time. Experiments were quenched by the addition of 20μL of 10% aqueous TFA. 5 μL of internal standard (1 mMdansyl-Tyr-Val-Gly-OH) was added, and experiments were diluted up to 100μL with 0.1% aqueous TFA. These assays were loaded onto apreequilibrated Harvard C₁₈-spin column (250 uL), which had previouslybeen wet with 2×300 μL of 50% acetonitrile in 0.1% aqueous TFA and 2×300μL of 0.1% aqueous TFA respectively, centrifuging at 300 g for 2 minbetween each 300 μL aliquot. Quenched plasma assays were centrifuged at300 g until the sample was loaded. The resultant filtrate was reloadedonto the column along with 100 μL of 0.1% aqueous TFA and centrifuged at300 g two additional times. The desired plasma peptide was washed by theaddition of 2×300 μL of 0.1% aqueous TFA and centrifuged at 300 g for 2min, discarding the filtrate after each wash. The desired peptide wereeluted by the addition of 300 μL of 40% acetonitrile (human plasma) in0.1% aqueous TFA and centrifugation at 300 g for 2 min. Eluted sampleswere diluted with 0.1% aqueous trifluoroacetic acid prior to analysis byC₁₈-RP-HPLC. To analyze the remaining percentage of 5 in plasma,incubations of 5 in plasma were immediately quenched, worked up, andanalyzed by C₁₈ RP-HPLC, and the ratio of apelin peptide to internalstandard was calculated based on the area under the peaks. This 0 minincubation ratio was used to compare the apelin peptide/internalstandard ratios for the time experiments. FIG. 13 shows thebreakdown-fragments (1-3 and 4-17) after plasma incubation ofapelin-17A2 (compound 5).

Example 15

The kinetic parameters for the KLKB1 cleavage was determined bymonitoring the decrease of parent peptide upon incubation of recombinanthuman KLKB1 (rhKLKB1) with native apelin-17 (2) as well as ACE2 andNEP-stabilized apelin A2 peptides 5 and 11, according to the NeprilysinQualitative Cleavage Assays and Plasma Kallikrein KLKB1 QualitativeCleavage Assays described herein.

Table 4 shows the kinetic parameters for NEP and KLKB1 cleavage ofcardiovascular active peptides.

TABLE 4 Substrate Enzyme K_(m) (μM) k_(cat) (1/S) k_(cat)/K_(m) (1/MS) 2 NEP 190 ± 40  3.4 ± 0.3 (1.8 ± 0.4) × 10⁴  2 KLKB1 97 ± 21 13.7 ±1.3  (1.4 ± 0.3) × 10⁵  5 KLKB1 30 ± 4  1.4 ± 0.2 (4.7 ± 0.8) × 10⁴ 11KLKB1 245 ± 75  16.5 ± 2.1  (6.7 ± 1.0) × 10⁴ Kininogen* KLKB1 0.750.031 4.1 × 10⁴ Factor XII* KLKB1 2.4 0.001 4.2 × 10² *Data obtainedfrom Gozzo, A. J. et.al.; “Heparin modulation of human plasma kallikreinon different substrates and inhibitors;” Biol. Chem. 2006, 387,1129-1138.

The KLKB1 cleavage kinetics are similar to those of neprilysin (NEP),which cleaves within the critical ‘RPRL’-motif, thereby inactivatingapelin. KLKB1 processes apelin-17 (2) and peptides 5 and 11 withmoderate efficiency (k_(cat)/K_(m)˜10⁵), comparable to othercardiovascular active peptide substrates. As the potent peptide 11,which is resistant to ACE2 and neprilysin, is degraded quickly, thisstimulated an endeavor to explore a stabilization strategy closer to theArg3-Arg4 cleavage site.

Example 16 Synthesis of Apelin-14A2 (54)

Resin bound BrF was subjected to manual SPPS, introducing amino acids inthe following order: Fmoc-Aib-OH, Fmoc-Nle-OH, Fmoc-Pro-OH, Fmoc-Gly-OH,Fmoc-Lys(Boc)-OH, Fmoc-His(Trt)-OH, Fmoc-Ser(t-Bu)-OH, Fmoc-Leu-OH,Fmoc-Arg(Pbf)-OH, Fmoc-Pro-OH, Fmoc-Arg(Pbf)-OH, Fmoc-Glu(Trt)-OH,Fmoc-Arg(Pbf)-OH). A portion (0.05 mmol) of resin-bound peptide wascleaved as previously described and purified using a C18 RP-HPLCanalytical column (method A), eluting at 14.4 min. The desired peptidewas isolated as a white solid after lyophilization (9.0 mg, 11%).Monoisotopic MW (MALDI-TOF) calculated for C₇₅H₁₂₄BrN₂₇O₁₇ 1753.9, found[M+H]⁺ 1753.6.

Example 17 Synthesis of Apelin-NMe14A2 (55)

Resin bound BrF was subjected to manual SPPS, introducing amino acids inthe following order: Fmoc-Aib-OH, Fmoc-Nle-OH, Fmoc-Pro-OH, Fmoc-Gly-OH,Fmoc-Lys(Boc)-OH, Fmoc-His(Trt)-OH, Fmoc-Ser(t-Bu)-OH,Fmoc-Arg(Boc₂)-NMeLeu-OH,¹² Fmoc-Pro-OH, Fmoc-Arg(Pbf)-OH,Fmoc-Glu(Trt)-OH, Fmoc-Arg(Pbf)-OH). A portion (0.05 mmol) ofresin-bound peptide was cleaved as previously described and purifiedusing a C18 RP-HPLC analytical column (method A), eluting at 14.7 min.The desired peptide was isolated as a white solid after lyophilization(7.5 mg, 9%). Monoisotopic MW (MALDI-TOF) calculated for C₇₆H₁₂₇BrN₂₇O₁₇1768.9, found [M+H]⁺ 1768.7.

Example 18 Synthesis of PALM-17A2 (56)

Compound 54 was extended by SPPS, introducing amino acids in thefollowing order: Fmoc-Arg(Pbf)-OH, Fmoc-Phe-OH, Fmoc-Lys(Boc)-OH,palmitic acid. A portion (0.05 mmol) of resin-bound peptide was cleavedas previously described and purified using a BiPhe RP-HPLC analyticalcolumn (method A), eluting at 25.8 min. The desired peptide was isolatedas a white solid after lyophilization (5.0 mg, 8%). Monoisotopic MW(MALDI-TOF) calculated for C₁₁₂H₁₈₈BrN₃₄O₂₁ 2424.4, found [M+H]⁺ 2423.9.

Example 19 Synthesis of PEG-17A2 (57)

Compound 54 was extended by SPPS, introducing amino acids in thefollowing order: Fmoc-Arg(Pbf)-OH, Fmoc-Phe-OH, Fmoc-Lys(Boc)-OH,Fmoc-(PEG)₆ propionic acid. A portion (0.05 mmol) of resin-bound peptidewas cleaved as previously described and purified using a BiPhe RP-HPLCanalytical column (method A), eluting at 25.6 min. The desired peptidewas isolated as a white solid after lyophilization (6.5 mg, 9%).Monoisotopic MW (MALDI-TOF) calculated for C₁₂₆H₁₉₇BrN₃₅O₂₉ 2743.4,found [M+H]⁺ 2743.2.

Example 20 Synthesis of PALM-NMe17A2 (58)

Compound 55 was extended by SPPS, introducing amino acids in thefollowing order: Fmoc-Arg(Pbf)-OH, Fmoc-Phe-OH, Fmoc-Lys(Boc)-OH,palmitic acid. A portion (0.05 mmol) of resin-bound peptide was cleavedas previously described and purified using a BiPhe RP-HPLC analyticalcolumn (method A), eluting at 17.2 min. The desired peptide was isolatedas a white solid after lyophilization (5.5 mg, 7%). Monoisotopic MW(MALDI-TOF) calculated for C₁₁₃H₁₉₀BrN₃₄O₂₁ 2438.4, found 2438.0.

Example 21 Synthesis of PEG-NMe17A2 (59)

Compound 55 was extended by SPPS, introducing amino acids in thefollowing order: Fmoc-Arg(Pbf)-OH, Fmoc-Phe-OH, Fmoc-Lys(Boc)-OH,Fmoc-(PEG)₆ propionic acid. A portion (0.05 mmol) of resin-bound peptidewas cleaved as previously described and puri-fied using a BiPhe RP-HPLCanalytical column (method A), eluting at 17.1 min. The desired peptidewas isolated as a white solid after lyophilization (6.5 mg, 8%).Monoisotopic MW (MALDI-TOF) calculated for C₁₂₇H₁₉₉BrN₃₅O₂₉ 2757.4,found 2757.4.

Example 22 In Vitro Stability Tests

The in vitro KLKB1 and NEP stability of the PALM/PEG peptides 56-59 wascompared to native apelin-17 (2), the A2 substituted peptide 5 and theNEP-resistant peptide 11. Peptides 56-59 were incubated with KLKB1(rhKLKB1, Novoprotein) or recombinant human NEP (rhNEP, Sino Biological)at 37° C. for up to 72 h.

Plasma Kallikrein KLKB1 Qualitative Cleavage Assays

Native apelin-17 (2) and apelin peptides 5, 56, 57, 58 and 59 weredissolved in Milli-Q water (1 mM). Human plasma kallikrein KLKB1 wereeach reconstituted in Tris buffer (100 mM TrisHCl, 10 mM CaCl2, 150 mMNaCl) and diluted with Tris buffer (50 mM TrisHCl, 250 mM NaCl) to givea KLKB1 concentration of 2 ng/μL. The KLKB1 enzyme was then preincubatedat 37° C. for 10 minutes prior to the addition of 5 μL of apelin peptide(1 mM). Aliquots (1 μL) were taken at 1, 2, 4, 6, 12, 24, 36, and 48hours and analyzed with MALDI-TOF mass spectrometry to qualitativelydetermine the time point at which degradation products could be observed(Table 4).

Neprilysin Qualitative Cleavage Assays

Native apelin-17 (2) and apelin peptides 5, 54, 56, 57, 58 and 59 weredissolved in Milli-Q water (1 mM). Recombinant Human Neprilysin (rhNEP,Sino Biological) was reconstituted in Tris buffer (100 mM Tris, 100 mMNaCl, 10 mM ZnCl₂, pH 7.5). To initiate the assays, rhNEP was diluted inTris buffer to a 2 ng/μL final concentration, and pre-incubated at 37°C. for 10 minutes prior to the addition of 5 μL of apelin peptide (1mM). Aliquots (1 μL) were taken at 1, 2, 4, 6, 12, 24, 36, and 48 hoursand analyzed with MALDI-TOF mass spectrometry to qualitatively determinethe time point at which degradation products could be observed. Table 5shows the timepoints at which degradation products of apelin peptidescould first be observed through MALDI-TOF after incubation with KLKB1and Neprilysin.

TABLE 5 Degradation Degradation Onset Onset Timepoint Timepoint PeptideModification with NEP with KLKB1  2 Apelin-17 <30 min <30 min  5Apelin-17A2 <1 hr <30 min 54 Apelin-14A2 >36 hr — 56 PALM-17A2 1 hr 1 hr57 PEG-17A2 12 hr 1 hr 58 PALM-NMe17A2 >36 hr 2 hr 59 PEG-NMe17A2 >36 hr2 hr

Quantitative Degradation Assays (Kinetics)

The extent of degradation was analyzed via LC-MS because of theoverlapping elution patterns of peptide fragments (NEP).

Native apelin-17 (2) and apelin peptides 5, 54, 56, 57, 58 and 59 weredissolved in Milli-Q water (1 mM). Recombinant human neprilysin (rhNEP,Sino Biological) was reconstituted in Tris buffer (100 mM Tris, 100 mMNaCl, 10 μM ZnCl₂, pH 7.5). To initiate the assay, rhNEP was diluted inTris buffer (3.1 nM final concentration) and preincubated at 37° C. for10 min prior to the addition of 5 μL of apelin peptide (1 mM) and 1.5 μLof internal standard dansyl-Tyr-Val-Gly-OH (1 mM). Aliquots (10 μL) wereremoved at 0, 1, 4, 24, and 72 h, quenched with 0.1 M EDTA (10 μL),diluted to 100 μL with Milli-Q water, and analyzed by LC-MS. Assays wereperformed in triplicate (n=3) for each time point. Integrated peak areasof the parent apelin peptide and internal standard derived from LC-MSanalyses were extracted using Mass Hunter software (version B.04.00) andcompared in positive extracted ion count modus (+EIC). The extent ofproteolysis was determined by comparing the initial (0 h) ratio of theintegrated extracted ions of the parent apelin peptide to the internaldansyl-YVG standard (apelin/dansyl-YVG) to the same ratio at thedifferent assay time points. The decrease in apelin/dansyl-YVG ratio wasconverted to a percentage of cleaved peptide over time.

Ca2+ Mobilization Assay

To study the extent to which the newly derived peptides triggerAPJ-receptor activation, a fluorescence coupled calcium release assayincluding a recombinant human APJ-Gal 6 receptor cell line was used.

Chem-5-APJ cells (Millipore, USA) were seeded (30 000 cells/well) intoNunclon Delta Surface 96-well, clear-bottom microtitre plates (ThermoScientific, Denmark) 24 hours prior to assay. Cells were loaded for 1hour with FLIPR Calcium 6-QF fluorescent indicator dye (MolecularDevices, USA) in assay buffer [Hanks balanced salt solution (HBSS), 20mM HEPES, 0.2% DMSO, 2.5 mM probenecid, pH 7.6], washed three times withassay buffer, then returned to the incubator for 10 min before assay ona fluorimetric imaging plate reader (FLIPR; Molecular Devices,Sunnyvale, Calif., USA). Maximum change in fluorescence over baselinewas used to determine agonist response. Dose-response curve data werefitted to a four-parameter logistic equation using PRISM (GraphPad, USA)from which pEC50 values were calculated. FIGS. 14A-G show theconcentration response curves of apelin peptides. Table 6 shows thepeptide half-life and receptor activation of studied Apelin peptides.

TABLE 6 t_(1/2) t_(1/2) t_(1/2) (rhNEP, (rhKLBB1, (hplasma, EC₅₀ ApelinModification h) h) h) (nM)  2 Apelin-17 0.4 0.4 0.02 N.D.  5 Apelin-17A21.0 0.7 0.3 4.0 ± 0.2 11 NMeLeu-17A2 >30 0.9 1.2 N.D. 54 Apelin-14A2 — —— 568 ± 34  55 NMeLeu14A2 — — — 176 ± 21  56 PALM-17A2 1.5 1.0 4.5 2.6 ±0.2 57 PEG-17A2 >30 1.4 18 6.3 ± 0.4 58 NMeLeu- >30 2.1 20.5 11.3 ± 2.1 PALM17A2 59 NMeLeu- >30 2.9 27 2.5 ± 0.2 PEG17A2

Compounds 56-59 feature EC50 values in the low nanomolar rangecomparable to the N-terminally free apelin-17A2 peptide (i.e., compound5). Unlike palmitoylation within the apelin peptide sequence, which canbe detrimental for receptor binding (Juhl, et al., “Development ofpotent and metabolically stable APJ ligands with high therapeuticpotential;” ChemMedChem 2016, 11, 2378-2384.), N-terminal extension by apalmitoyl or PEG chain seems not to affect receptor binding andinternalization. Surprisingly, the 14-mer left after the KLKB1 cut(i.e., compound 54 and 55), seems to be rather inactive featuring a200-times higher EC50 than the 17-mers.

Example 23 Physiological Test-Blood Pressure Assays

Apelin peptides 11, 56-59 as well as the KLKB1-cleavage fragments 54 and55 were tested for blood pressure lowering abilities in anesthetizedmice.

Mice were anesthetized with 1.5% isoflurane/oxygen, and body temperaturewas monitored and maintained at 36° C. by a heating pad. The aorta wascannulated via the right carotid artery using a PV loop catheter (model1.2F from Scisense, Transonic) in order to continuously record arterialblood pressure and heart rate (LabScribe 2.0, Scisense). Compounds 11,and 54-59 or 55-59 (1.4 μM/kg body weight) or the same volume of salinewas injected via the right jugular vein. Results are reported assystolic blood pressure (SBP), diastolic blood pressure (DBP), meanarterial blood pressure (MABP), and heart rate (HR) shown in FIGS.15A-D.

Apelin peptides were delivered systemically via the right internaljugular vein while blood pressure (BP) and heart rate (HR) werecontinuously monitored in the aorta cannulated via the right carotidartery. All N-terminally extended apelin peptides, except 58, showpronounced and time-stable blood pressure lowering effects (FIGS. 15a-d). Among the synthesized peptides 56-59, peptide 58 triggers also thelowest Ca²⁺ mobilization (Table 5). Interestingly, the heart rateincreasing effect is restored in this peptide 58, suggesting alternativeactivation pathways. In this regard, peptides 56, 57 and 59 are morepotent than apelin-17 (2) and apelin-17A2 (5). Importantly, bothPEGylated peptides 57 and 59 show the most stable and potent effect. Incontrast, both the fragments left after KLKB1 cleavage (peptides 54 and55) are inactive or nearly so in their cardio-physiological effects(FIGS. 16A-B). This correlates with the results obtained from the Ca²⁺mobilization assay.

Human plasma kallikrein (KLKB1) has been identified as human proteasethat cleaves apelin-17 relatively quickly between Arg3-Arg4. Theresulting C-terminal 14-mer appears to be poor with regard to Ca²⁺mobilization (APJ receptor activation capacity) and is lackingbeneficial cardio-physiological effects. Hence KLKB1 degradationinactivates apelin 17. N-terminally extension by a palmitoyl or PEG6chain yields apelin peptides that are more cleavage resistant towardsboth KLKB1 and NEP proteases and have prolonged plasma half-life.Combined with their potent and prolonged blood pressure lowering effect,these new apelin peptides present a promising new target for thedevelopment of cardiovascular active peptide drugs. Furtherphysiological studies and other synthetic stabilization approaches arecurrently underway to obtain a better understanding of the impact ofthis new cleavage site for the design of novel drug targets.

Example 24 Cardiac Allograft Vasculopathy

B6 male hearts were transplanted heterotopically into male or female B6of the recipient mice, starting 2 weeks after transplant. Synthesizedapelin peptide (Apelin-NMe17A2) (11), was given by daily intraperitonealinjection (3 mg/kg/d) for 4 weeks. Female mice raise immune responseagainst the male HY antigen, injure the coronary arteries of thetransplanted heart based on Verhoeff-Van Gieson staining (FIG. 17)leading to progressive expansion of the arterial intima occluding thearterial lumen (FIG. 18). Treatment with apelin peptide mitigatesarteriopathy vs saline-treated carrier controls (a-b). *p<0.05 comparedwith carrier/placebo group. n=6; M=male; F=female. The resultsdemonstrate that treatment with apelin peptides of the present inventionmay protect against transplant arteriopathy.

C57BL/6J mice were purchased from Jackson Laboratories. The C57BL/6 micesubjected to surgery were 11-14 weeks old. All animal experiments werecarried out according to the Canadian Council on Animal Care Guidelines.Animal protocols were approved by the Animal Care and Use Committee atthe University of Alberta. Hearts from 12-14 weeks male wild-type (WT)donors were transplanted heterotopically to the abdomen of the female WTrecipients. The inferior and superior vena cavae, and the pulmonaryveins of the donor heart were ligated. Then the donor aorta andpulmonary artery were anastomosed to the recipient's abdominal aorta andinferior vena cava, below the renal arteries. Cardiac allograftvasculopathy (CAV) was induced due to the presence of HY-minorhistocompatibility antigen-directed, cell-mediated allo-immune responseagainst the male donor hearts. The heart grafts were harvested six weeksafter transplantation. Intima area, endothelial loss in medium tolarge-sized arteries, inflammatory cellular infiltration,microvasculature density and tip cell markers using Immunohistochemistryand qPCR were characterized.

Example 25 Apelin Peptide Prevents Angiotensin II-Induced AorticAbdominal Aneurysm

Experimental Animals and Protocols. Male LDL receptor deficient(Ldlr^(−/−)) mice were generated and bred in C57BL/6 background. Allanimal experiments were carried out in accordance with the CanadianCouncil on Animal Care Guidelines, and animal protocols were reviewedand approved by the Animal Care and Use Committee at the University ofAlberta.

Angiotensin II (Ang II) and Phenylephrine (PE) Infusion In Vivo.

Alzet micro-osmotic pump (model 1002 or 1004; Durect Co.) was implantedsubcutaneously at the dorsum of the neck to infuse Ang II (1.5mg/kg⁻¹d⁻¹) or vehicle (saline) for 28 days in high fat fed Ldlr^(−/−)mice.

Histological Analyses, Terminal Deoxynucleotidyl Transferase dUTP NickEnd Labeling (TUNEL) and Immunofluorescence Staining.

After 4 weeks of Ang II or saline infusion, mice underwent whole bodyperfuse-fixation, via the left ventricle, with 10% buffered formalin (80mmHg, 20 min). Third order mesenteric arteries were dissected outcarefully without being forced or over stretched, preserved in 10%buffered formalin for 48 hours and embedded in paraffin. Aortas weredissected, imaged for gross morphological assessment, then fixed informalin and paraffin-embedded. Five micrometer thick formalin fixedparaffin embedded (FFPE) sections of aortas and mesenteric arteries werestained for Movat's pentachrome and Gomori Trichrome to evaluatemorphological alternations. Collagen positive area was quantified by themorphometric analysis using the Metamorph Basic (version 7.7.0.0)software. In situ DNA fragmentation was detected in 5-μm thick FFPEsections of aorta using the commercially available terminaldeoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)assay kit according to manufacturer's instructions (Invitrogen) aspreviously described. Five-micrometer thick FFPE sections were also usedfor the immunofluorescence staining for ACE2, calponin and apelin.Thickness of the medial layer of the aorta was measured in calibratedimages as the mean distance between the external elastin lamella and theinternal elastin lamella from 8 randomly selected fields of thecross-section of an aorta using the Metamorph Basic software (version7.7.0). Calponin positive cells in the aorta were quantified to estimatethe VSMC density.

Dihydroethidium (DHE) Staining and Nicotinamide Adenine DinucleotidePhosphate (NADPH) Oxidase Activity Assay.

For DHE and NADPH staining, fresh aortas were collected (withoutperfuse-fixation) and preserved in OCT at −80° C. Nicotinamide adeninedinucleotide phosphate (NADPH) oxidase activity in human or mice primaryaortic VSMCs was quantified by lucigenin enhanced chemiluminescenceusing a single-tube luminometer (Berthold FB12, Berthold Technologies,Germany) modified to maintain the sample temperature at 37° C. aspreviously described. Briefly, after three times of wash in ice-coldphosphate buffered saline (PBS) with protease and, VSMCs or OCT-embeddedaorta sections were lysed with RIPA buffer containing protease andphosphatase inhibitor cocktails. NADPH (1 mM) and Lucigenin (50 μM) wereadded to 100 μg of protein extracts in the presence or absence ofdiphenylene iodonium (DPI; 10 μM), a selective inhibitor offlavin-containing enzymes including NADPH Oxidase. Light emission wasmeasured every 1 second during a 5-minute period using a single-tubeluminometer (Berthold FB12, Berthold Technologies, Germany) at 37° C.The emission over a 3-minute period was averaged for each sample.

Dihydroethidium (DHE) staining was performed on aortic SMCs andOCT-embedded aorta sections and visualized under fluorescence microscope(Olympus IX81). For SMCs, after 1 hour of incubation with or without AngII (1 μM), cells were incubated with DHE (20 μM DHE, final concentrationin culture media; Sigma Aldrich) at 37° C. for 30 minutes in dark.Fluorescence images were subsequently captured with a fluorescencemicroscope (IX81, Olympus) after washing with PBS. Quantitativemeasurements of DHE fluorescence intensity were carried out usingMetamorph Basic (version 7.7.0.0), regions congruent to the cell nucleiboundaries were drawn, the average pixel intensities were calculated andcorrected by subtracting the background, and reported here as DHEfluorescence.

Ultrasonic Vasculography.

Ultrasonic images of the aortas were obtained in mice anesthetized with1.5% isoflurane using a Vevo 2100 high resolution-imaging systemequipped with a real time microvisualization scan head (RMV 704, VisualSonics, Toronto, Canada). The aortic diameters were measured by M-modeat thoracic aorta, aortic arch and abdominal aorta. The maximum aorticlumen diameter (corresponding to cardiac systole) and the minimum aorticlumen diameter (corresponding to cardiac diastole) recordings weremeasured and used to calculate the aortic expansion index [(systolicaortic diameter-diastolic aortic diameter)/systolic diameterx 100].

Western Blot Analysis.

Protein was extracted from aorta using RIPA lysis buffer containingprotease and phosphatase inhibitor cocktails, and quantified using theBCA Protein Array Kit (Pierce, Rockford, Ill.). Equal amounts of proteinextracts were loaded and separated by SDS-PAGE gel and then transferredto polyvinylidene fluoride (PVDF) membranes. The membranes were blockedfor 1 hour at room temperature with 5% skim milk in TBST, and thenincubated with primary antibodies overnight at 4° C., followed byHRP-linked secondary antibodies. The probed proteins were detected withAmersham ECL Prime detection reagent and visualized with ImageQuant LAS4000 Mini Biomolecular Imager (GE Healthcare, Baie-d'Urfé, QC, Canada).The expression levels of target proteins were quantified by densitometryusing the equipped software. Equal loading of protein was confirmed bystaining the membrane with Pierce™ Reversible Protein Stain Kit for PVDFMembranes (ThermoFisher Scientific, USA).

Apelin Peptide and Aortic Aneurysm.

Male Ldlr^(−/−) mice (Jackson Lab) received high fat diet (EnvigoTD.88137) at 8 weeks of age and throughout the study. One week afterinitiating high fat diet, osmotic pumps (Model 1004, Alzet) wereimplanted subcutaneously to deliver Angiotensin II (Sigma-Aldrich) at arate of 1.5 mg/kg/d for 28 days. Synthesized apelin peptide 11 was givenby daily intraperitoneal injection (3 mg/kg/d) for 28 days.

The data is shown in FIGS. 19-25. As shown in these Figures,NEP-resistant apelin peptide 11 (Apelin-NMe17A2) markedly prevented theformation of abdominal aortic aneurysm suggesting that apelin peptidesrepresents a new class of drugs for this condition which currently hasno current medical therapy.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. A peptidomimetic having the formula:Cbz-NHCH₂CH₂—(OCH₂CH₂)_(m)—CO-Lys-Phe-Arg-Arg-Gln-aa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa′15-aa′16-aa′17,or pharmaceutically acceptable salts thereof, wherein m is 3 to 10;wherein each of aa′6, aa′7, aa′8, aa′9, aa′10, aa′11, aa′12, aa′13,aa′14, aa′15, aa′16 and aa′17 is independently an amino acid, wherein:aa′6 comprises Arg or a conservative variant thereof; aa′7 comprises Proor a conservative variant thereof; aa′8 comprises an amino acid or aconservative variant thereof selected from the group consisting of Arg,Arg-D, αMeArg and azaArg; aa′9 comprises an amino acid or a conservativevariant thereof selected from the group consisting of Leu, NMeLeu,αMeLeu and azaLeu; aa′10 comprises Ser or a conservative variantthereof; aa′11 comprises His or a conservative variant thereof; aa′12comprises Lys or a conservative variant thereof; aa′13 comprises Gly ora conservative variant thereof; aa′14 comprises Pro or a conservativevariant thereof; aa′15 is comprises Nle or a conservative variantthereof, wherein Nle is norleucine; aa′16 is comprises Aib or aconservative variant thereof, wherein Aib is α-aminoisobutryic acid; andaa′17 is comprises paraBrPhe or a conservative variant thereof. 9.(canceled)
 10. (canceled)
 11. (canceled)
 12. (canceled)
 13. Thepeptidomimetic of claim 8, whereinaa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa′15-aa′16-aa′17 isArg-Pro-Arg-D-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.
 14. Thepeptidomimetic of claim 8, whereinaa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa′15-aa′16-aa′17 isArg-Pro-Arg-NMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.
 15. Thepeptidomimetic of claim 8, whereinaa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa′15-aa′16-aa′17 isArg-Pro-αMeArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.
 16. Thepeptidomimetic of claim 8, whereinaa′6-aa′7-aa′8-aa′9-aa1l-aa′11-aa′12-aa′13-aa′14-aa′15-aa′16-aa′17 isArg-Pro-Arg-αMeLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.
 17. Thepeptidomimetic of claim 8, whereinaa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa′15-aa′16-aa′17 isArg-Pro-azaArg-Leu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.
 18. Thepeptidomimetic of claim 8, whereinaa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa′15-aa′16-aa′17 isArg-Pro-Arg-azaLeu-Ser-His-Lys-Gly-Pro-Nle-Aib-paraBrPhe.
 19. (canceled)20. The peptidomimetic of claim 8 having the following structure:

wherein m is from 3 to
 10. 21. (canceled)
 22. (canceled)
 23. (canceled)24. (canceled)
 25. A composition comprising the peptidomimetic havingthe formula:Cbz-NHCH₂CH₂—(OCH₂CH₂)_(m)—CO-Lys-Phe-Arg-Arg-Gln-aa′6-aa′7-aa′8-aa′9-aa′10-aa′11-aa′12-aa′13-aa′14-aa′15-aa′16-aa′17,or pharmaceutically acceptable salts thereof; wherein m is 3 to 10;wherein each of aa′6, aa′7, aa′8, aa′9, aa′10, aa′11, aa′12, aa′13,aa′14, aa′15, aa′16 and aa′17 is independently an amino acid, wherein:aa′6 comprises Arg or a conservative variant thereof; aa′7 comprises Proor a conservative variant thereof; aa′8 comprises an amino acid or aconservative variant thereof selected from the group consisting of Arg,Arg-D, αMeArg and azaArg; aa′9 comprises an amino acid or a conservativevariant thereof selected from the group consisting of Leu, NMeLeu,αMeLeu and azaLeu; aa′10 comprises Ser or a conservative variantthereof; aa′11 comprises His or a conservative variant thereof; aa′12comprises Lys or a conservative variant thereof; aa′13 comprises Gly ora conservative variant thereof; aa′14 comprises Pro or a conservativevariant thereof; aa′15 is comprises Nle or a conservative variantthereof, wherein Nle is norleucine; aa′16 is comprises Aib or aconservative variant thereof, wherein Aib is α-aminoisobutryic acid; andaa′17 is comprises paraBrPhe or a conservative variant thereof.
 26. Thecomposition of claim 25, wherein the composition is a pharmaceuticalcomposition.
 27. A method of modulating an apelin pathway disorder in asubject comprising administering to the subject a therapeuticallyeffective amount of an apelin peptide comprising a peptidomimetic havingthe formula of claim 8, or pharmaceutically acceptable salts thereof.28. The method of claim 27, wherein the apelin peptide is an apelinreceptor agonist.
 29. The method of claim 27, wherein the apelin pathwaydisorder is a cardiac disease.
 30. The method of claim 27, wherein thecardiac disease is selected from the group consisting of systemicarterial hypertension, abdominal aortic aneurysm, pulmonary arterialhypertension, heart failure, myocardial ischemic-reperfusion injury,cardiac allograft vasculopathy, myocardial infarction, and high bloodpressure.
 31. The method of claim 30, wherein the cardiac disease isabdominal aortic aneurysm.
 32. The method of claim 30, wherein thecardiac disease is cardiac allograft vasculopathy.
 33. The method ofclaim 27, wherein the administering is carried out intravenously.
 34. Amethod of modulating vascular tone in a subject comprising administeringto the subject an effective amount of an apelin receptor agonistcomprising a peptidomimetic of Formula (I) or Formula (II), orpharmaceutically acceptable salts thereof.
 35. The method of claim 34,wherein the administering is carried out intravenously.
 36. A method ofreducing cardiac reperfusion injury following myocardial infarction in asubject comprising administering to the subject an effective amount ofan apelin receptor agonist comprising an apelin peptide comprising apeptidomimetic having the formula of claim 8, or pharmaceuticallyacceptable salts thereof.
 37. The method of claim 36, wherein thecardiac reperfusion injury is due to an ischemic condition.
 38. Themethod of claim 36, wherein the ischemic condition is selected from thegroup consisting of acute coronary syndromes, thomboembolic events,surgery or resuscitation from cardiac arrest, and combinations thereof.39. The method of claim 36, wherein the administering step is carriedout intravenously.
 40. A method of reducing blood pressure in a subjectcomprising administering to the subject an effective amount of an apelinreceptor agonist comprising an apelin peptide comprising apeptidomimetic having the formula of claim 8, or pharmaceuticallyacceptable salts thereof.
 41. The method of claim 40, wherein theadministering step is carried out intravenously.